
Class 
Book. 



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18 



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COPYRIGHT DEPOSIT. 




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PRACTICAL 
ELECTRICITY 




Copyright 190I-I904-1908-I9II by QcveUnd Aimawre Works 



QUESTIO^IS AHP ANSWERS 

SIXTH EpmoN' 






\^ i ' 



Pv'ess of 

W. B. Conkcy Company 

Hammond, Ind. 






©CI.A28r,221 






INTRODUCTORY. 



In March, 1896, The Armature Winder made its first appear- 
ance, its attractive feature being the commencement of a series of 
lectures on designing dynamos and motors, these letters being 
written from daily shop practice, and made comprehensible by 
questions and their subsequent answers. As each paper with its 
lecture made its appearance, the interest manifested by readers 
became more pronounced, until we were flooded with inquiries for 
numbers which the various readers had missed. As we had only 
reserved a very few papers of each issue, our ability to supply 
the back numbers was limited. We consequently decided to 
print the lectures in book form, and so notified our readers of 
this decision, with the result that orders for the book came in, in 
quantities which were beyond anything we had anticipated. 
This evidence of the popularity of our efforts encouraged us in 
compiling a work much more extensive and valuable than had at 
first been our intention. In order to accomplish this, we felt the ne- 
cessity of associating with us a man of greater technical knowledge 
than we ourselves possessed, so that the work might be thoroughly 
criticised and enlarged. We selected Mr. John C. Lincoln, an 
electrical engineer of national reputation, who has contributed 
articles to this book covering matters of great interest, and, so far 
as we have been able to learn, ideas never before appearing in 
print. We are obligated to Mr. C. E. F. Ahlm for assistance 
rendered in preparing the chapter on electric automobiles. 

CLEVELAND ARMATURE WORKS. 

Clevelaiid. Ohio, 1911. James L. Mauldin / p^^p^ 

Alvin a. Pifer \ PROP^. 



PiRKFACE. 

This book was i^ritten especially to assist those who 
have some practical knowledge of electricity and who wish 
to learn more of the way in which wiring* is calculated and 
of the simpler and more important parts of dynamo electric 
machine design. Some of the methods used and explana- 
tions advanced in the book are, so far as the writers know, 
entirely new, and it has all been written with the idea of 
illustrating the subject and making it las simple and as easy 
of comprehension as possible. The only way to obtain a 
working knowledge of the subject is by careful study. The 
book has been arranged so that those who are willing to 
devote some effort to the work can get a clear conception 
of the more importlant ideas and laws that underlie the sub- 
ject. One who studies the text and answers the questions 
at the end of each chapter should be able to calculate a 
wiring job for lig-hts or power; to calculate the proper size 
and amount of wire for a dynamo when he has the dimen- 
Bions of the niaehine; to calculate the size and winding for 
0, magnet to give a required pull, etc. 

The table of contents shows the scope of the work. 

The q''jestions which follow each chapter, in connection 
with the answers, will bring out the more important points 
treated in each chapter. It is believed that a careful study 
of the text and the working of the examples will serve to 
throi;^ a great deal of light upon a subject in which a grea/t 
many people are interested. Tlie dictionary in connection with 
this work is a valuable feature. 

Houston's Electrical* dictionary was largely used in the 
preparation of same. 

CLEVELAND ARMATURE WORKS. 

CLEVELAND. OHIO. 



TABLE OF CONTENTS 



CHAPTER I. 
II. 
III. 
IV. 
V. 
VI. 
VII. 
VIII. 
LX. 
X. 
XI. 
XII. 
XIII. 
XIV. 
XV. 

XVI. 

XVII. 
XVIII, 
XIX. 
XX. 



Wiring. 

Electric Batteries. Electro Plating. 

Magnetism. 

The Magnetic Circuit. 

Magnetic Traction. 

Magnetic Leakage. 

Energy in Electric Circuits, 

Calculation of Size of Wire for Magnetizing Coils. 

Calculation of E. M. F.'s in Electric Machines. 

Counter E. M. F. 

Hysteresis and Eddy Currents. 

Armature Reaction. 

Sparking. 

Winding of Dynamos and Motors. 

Proper Method of Connecting Dynamos and Motors. 

Self Excatation. 
Diseases of Dynamos and Motors, their Symptoms 

and how to cure them . 
Arc and Incandescent Lamps, 
Measuring Instruments. 
Alternating Current, 
Electric Automobiles. 



A 



CHAPTER I. 
VVIKIJVG. 

1. It is very commonly said that nothing is known of 
electricity. Tliis is both true and false. We do not know 
what electricity is nor anything of its ultimate nature, but 
we do know a great deal about the laws which govern the 
action of electricity. 

For all ordinary purposes the action of electricity is 
very closely analogous to that of water. From the 
study of the principles which govern the flow and action of 
water a very great deal can be learned concerning the prin- 
ciples and laws governing the action of electricity. 

In this analogy the water represents electricity. When 
water flows from a higher to a lower level, it is capable of 
doing work by driving some kind of a water wheel. The 
greater the height through which the water falls, the 
greater the amount of work it can do. The same thing is 
true of electricity. The greater the difference in electrical 
level, or difference of potential, or the greater the voltage, 
the greater the amount of electrical work the electricity can 
do. The unit of difference of electrical level is the volt, and 
we may say that the volt corresponds to one foot of "head" 
in a system for developing power by water. The amount of 
power that can be developed from a water fall depends on 
two things; flrst, the fall in feet or the head, and second, 
the size of the stream. At Niagara Falls the power that can 
be developed is practically infinite, not because the height 
of the fall is so great, but because the size of the stream is 
so great. Any water fall is capable of developing power, 
depending on the size of the stream. The unit of flow may 



2 

be taken as one gallon per second. The corresponding- 
quantity in electricity is called current. The unit of cur- 
rent is called the ampere. The ampere then corresponds to 
the one gallon per second in a flow of water. 

The amount of water that can flow from a higher to 
a lower level depends on the size of the pipe line through 
which the water is led. Imagine a large pond of water 
twenty-five feet above the sea. The amount of water that 
will flow from the pond through a 4-inch pipe is very much 
greater than what will flow through a J^-inch pipe. Again 
if there are two pipes of the same size leading from the 
pond to the sea and one is twice as long as the other, afbout 
twice as much water will flow through the short pipe as 
through the long one. The friction of the water is greater 
in the long pipe, or the resistance to the flow is greater, and 
so less water flows. 

There is no convenient unit for the resistance of a pipe 
to the flow of water, but the unit of resistance of a wire to 
carrying a current is well defined and is called the ohm. 





Figure 1 

Resistance offered to flow of water through a long crooked pipe. 
Discharge in gallons per minute corresponding to amperes. 



^ 3 

The resistance offered by the long, small, ^crooked pipe 
to the flow of the "water corresponds to the resistance of- 
fered by a wire to the flow of the electrical current. An in- 
spection of Fig. 1 will show that the flow depends on the 
head. If, instead of having a head of 25 feet, it was in- 
creased to 50 feet, the amount of water discharged would be 
doubled, so that the flow depends on the head or pressure. 
If on the other hand the discharge pipe was made larger, 
or shorter, even with 25 feet head, twice as much water 
could be made to escape, so that the flow or current is in- 
versely proportioned to the resistance. 

Putting this in the form of an equation we have: 
Discharge or current equals head or pressure divided 
by resistance or friction. In a circuit carrying electricity 
the same thing is true and we have: Electrical discharge or 
current equals electrical head or pressure, divided by elec- 
trical friction or resistance. Since the unit of electrical 
current is the ampere, and the unit of electrical pressure is 
the volt, and the unit of electrical resistance is the ohm, we 
have: Amperes equal volts divided by ohms, or putting it in 
the form of a fraction we have: 

volts 
Am.peres equals 



ohm; 



This relation is known as Ohm's law and is one of the 
most important that we shall consider. Since the electrical 
pressure is what causes the movement of the electrical cur- 
rent, it is called electro-motive force, and as this term is 
very long it is abbreviated to E. M. F. Since the amperes 
measure the amount of flow of electricity, such flow is 



called current, ^nd this is abbreviated to C. Kesistance is 
abbreviated to R., and we have our Ohms law 

E. M. F. ^ E 

C equals (1); or C equals — 

R R 

when E. is used in place of E. M. F. 

By the way in which Oh,ms law was deduced it is plain 
to see that is is only one form of a general and universal 
law. 

Ohms law is the statement for electrical quantities of 
the general law that the result produced is proportional to 
the effort expended, and inversely proportional to the re- 
sistance to be overcome. 

To get a general idea of these units we may say that a 
single cell of storage battery has a voltage of two volts. 
One hundred and ten volts is the electrical pressure usually 
employed for lighting incandescent lamps. Two hundred 
and twenty volts is very frequently used as the E. M. F. for 
driving motors. Five hundred volts is universally used on 
street railroads to propel street cars. An ordinary gravity 
batter3% such as is usually employed for telegraphic work- 
has an E. M. F. of one volt. Dynamos for electrotyp- 
ing usually employ two or three volts. Dynamos for elec- 
trcplating from ^ve to ten volts. 

The current taken by an incandescemt lamp is about 
Yo ampere. The current required by a street arc lamp is 
from ten to six amperes, depending on the br'illiancy of the 
light. The current used in a land telegraph wire is .003 to 
.005 amperes. The resistance of 1,000 feet of copper wire 
one-tenth of an inch in diameter is one ohm. Ten 
feei of German silver wire the size of the lead in 
a pencil has a resistance of one ohm. The resist- 



5 



ance of a mile of the heavy feed wire used 
propelling street ears is about one-tenth of an ohm. 



m 




Figure 2 
System for distributing hot water at constant pressure. 

Suppose Fig. 2 to be part of the heating* system of a 
building'. The pump takes in the water from 
the low pressure pipe, and after passing* 
through a heater it is forced out into the 
high pressure pipe to the radiators over the building. If 
the pipes PI and PO are large enough there will be the same 
pressure practically at all parts of the pipe, and each radia- 
tor Rl, R2 and R3 will be exposed to the same pressure and 
receive the same amount of water provided they are simi- 
lar. If, however, the pipes PI and PO are small, some of the 
pressure on the water in the pipe PI will be lost in over- 
coming the friction of the pipe, so that radiator R3 farthest 
away from the pump would not get the same amount ol 
pressure as Radiator Rl nearest the pump. There would be 
a similar loss of pressure in pipe PO. If the pump produces 
a pressure of twenty pounds per square inch, and the fric- 
tion and resistance of the leading pipe PI is great enough 
to cause the pressure to fall to 19 pounds at the nearest 
radiator Rl, and causes it to fall to 18 pounds at R3, the 



6 



loss of pressure will be "two pounds at R3 in the pipe PO, 
and two pounds in the pipe P1 , if both PI and PO are ol the 
same size. The loss will be one pound at Kl in each pipe. 
Under these circumstances the pressure driving- water 
through El is 18 pounds and through R3 is 16 pounds, in- 
stead of 20 pounds as produced by the pump. Such a sys- 
tem for distributing water is closely analogous to a con- 
stant potential or constant electrical pressure system for 
distributing electricity. The pump takes the water from 
one main pipe and raises the pressure and delivers it to the 
other pipe. The radiators between t!hese pipes receive the 
water at practically constant pressure. The total stream in 
the main pipe is the sum of the individual currents in the 
radiators. The loss of head or pressure in t;he main pipes is 
greater as the flow of water is increased, and, if the radia- 
tors require practically constant pressure to work properly, 
soon reaches a limit. In each of these four respects such a 
water system is perfectly analogous to a constant potential 
lighting system. The pump corresponds to the dynamo in 
Fig. 3, which takes the electricity from one wire and raises 
its pressure so that it is 110 volts higher at one side of the 
dynamo than at the other. 




Figure 3. 
System for distributing electricity at constant pressure. 



The electricity is carried along the main wires Ml and 
MO, which correspond to the two pipes PI and PO in Fig. 
2, to the incandescent lamps LI, L2, L3. It is evident that 
there is some loss of pressure in carrying the current along 
the main wires MO and Ml from the dynamos to the lamps, 
and that this loss of pressure depends on the amount of cur- 
rent or upon the number of lamps in use. 

The lamp L3 will get in any case some less pressure 
than the lamp Ll, and when this difference becomes great 
enough so that L3 burns perceptibly dimmer than Ll, 
the main lines Ml and MO are carrying more current than 
they properly can. In practice the number of radiators in 
such a heating system as shown in Fig. 2 would not probably 
be much over 100, and usually very much less, while for the 
electric system the number of lamps on the dynamo will 
be from five to ten times as great. 




f 



M. 



^ 



O 



£3: 



3, 
O 

o 



TT 



s 



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. P' P 9 P 



§ 



YO 
:0 
O 
O 
O 
O 
O 
O 



Figure 4 
Typical constant potential system. 



Fig. 4 shows the dynamo taking current from the main 
MO and delivering it at 110 volts higher pressure to the main 
Ml. Part of it leaves the main Ml for the branch Bl and 
flows through the seven lamps to the other main MO. The 



8 

voltage is lost in overcoming the resistance of the lamps. 
The resistance of .the lamps constitutes from 90 to 98 per 
cent, of the resistance of the circuit. A second part leaves 
the main at B2 and passes into the wires of this 'branch 
through the 17 lamps shown. The rest of the current 
passes to B3 and through the 8 lamps in that circuit. There 
will, of course, be some loss of pressure or "drop" in the 
branch circuits. 

The calculation required in wiring is needed to find 
out how large to make the main wires MO and Ml and how 
large the wire on the branch circuits should 'be. The whole 
system should be so designed that there should be a differ- 
ence of only a volt or two between the various lamps on the 
circuit. The point to be aimed at is even or constant volt- 
age for the lamps. 

We will take up three different forms of Ohm's law ttiat 
will be convenient for use in calculating wiring problems. 

E. M. F. 

We have seen that C equals , or, put into words^ 

R 

amperes equal volts divided by ohms. 

The two other forms of this most important equatioi* 
are volts equals amperes multiplied by ohms; or 

E. M. F. equals' C multiplied by E. (2) ; and third, ohma 

E. M. F. 

equal volts divided by amperes; or, R equals (3). 

C 

These three equations should be carefully studied and 
memorized. For our work in wiring, the second is the most 



9 

important. Equation (2) means that the loss in volts in 
any part of the circuit depends on the amount of current 
the wire is carrying, and also on the resistance of the wire. 
If the amount of current carried is doubled, the volts lost 
are doubled; and if a new wire is used of twice the resist- 
ance, the loss of volts is doubled, and in general the volts 
lost or the "drop" is equal to the amperes the wire is carry- 
ing multiplied by the ohms of resistance of the wire car- 
r^ung the current. Suppose there were 100 lamps on the 
three circuits shown in Fig. 4 and that they were very 
close together, so that they all received about the same 
E. M. F. from the mains Ml and MO, but that the dynamo 
was about 500 feet from the lamps, near an engine. In 
such a case the principal loss of pressure would be in the 
mains carr^n'ng current between the dynamo and lamps. If 
w^e use Xo. 6 wire, which is .162 inches in diameter, there 
would be a resistance of .395 ohms in the mains, for there 
are 1,000 feet in the two mains, and the table No. 1 shows 
this. Each lamp requires Vi ampere, so that 100 lamps twill 
require 50 amperes. 

By formula 2 we have volts lost in leads or mains equal 
amperes multiplied by ohms, or drop, equals 50 multiplied 
by .395 equals 19.75 volts. In this case, if the lamps were 
to be supplied with 110 volts, the dynamo would have to 
produce 110 volts plus 19.75 volts, or 129.75 volts. Circuits 
of this sort are frequent, and if carefully operated such a 
grpat loss as 20 volts in the mains may be allowed. The 
ordinary case, however, is one in which the lamps are about 
equally distributed between the dynamo and the end of the 
circuit. In such a case a drop of 20 volts in the mains 
would not be permissible, for then the lamps near the 
dynamo would get 130 volts and those at the end of the 

9 



10 

circuit would get 110 volts. This is altogether too much varia- 
tion. The greatest variation that should ever be allowed is 8 
volts, and all well-regulated plants do not have more than 
two. The reason that it is best to have the variation a mini- 
mum is that the incandescent lamps have a much longer life if 
the voltage is constant than if it is not. If a lamp has a life of 
800 hours at 110 volts, it will not burn more than 200 hours at 
115 volts, and if it is burned at 105 volts it will not give more 
than 2-3 of its rated light. The drop usually allowed in mains 
for a building does not exceed 3 per cent., and in the best 
plants is not over 2 per cent. 

Table 1 gives the properties of copper wire of ail the 
American or B. & S. (Brown. & Sharpe) gauge sizes. 



. TABLE 1. 

PKOPERTIES OF PURE COPPER WIRE. 





AT 75 DEGREES FAHRENHEIT 


R. Ohms 

per 
1000 Feet 




1^^ 
1?^?. 


R. Ohms 

per 
1000 Feet 


Ohms 
per Mile 


Feet 
per Ohm 


Ohms per Lb. 


ih 


^%^ 


150° 


ii'^ 


0000 

000 

00 



1 


.04906 
.06186 
.07801 
.09831 
.12404 


.25903 
.32664 
.41187 
.51909 
.65490 


20383. • 
16165. 

12820. 
10409. 
8062.3 


.000076736 

.00012039 

.00019423 

.00030772 

.00048994 


.05675 

.07160 

.09028 

.1161 

.1435 


1 = 1 


2 
3 
4 
5 


.15640 
.19723 
.24869 
.31361 
.39546 


.82582 
1.0414 
1.3131 
1.6558 
2.0881 


6393.7 
5070.2 
4021.0 

3188.7 
2528.7 


.00078045 

.0012406 

.0019721 

.0031361 

.0049868 


.1810 
.2283 
.2879 
.3630 
.4577 




6 




7 
8 
9 

10 
11 


.49871 
.62881 
.79281 

1. 

1.2607 


2.6331 
3.3201 
4.1860 
5.2800 
6.6568 


2005.2 
1590.3 
1261.3 
1000.0 
793.18 


.0079294 

.012608 

.020042 

.031380 

.0.50682 


.5771 
.7278 
.9175 
1.157 
1.459 


' 


12 
13 
14 
15 
16 


1.5898 
2.0047 
2.5908 
3.1150 
4.0191 


8.3940 
10.585 
13.680 
16.477 
21.221 


629.02 

498.83 
385.97 
321.02 

248.81 


.080585 

.12841 

.20880 

.31658 

.51501 


1.840 
2.320 
2.998 
3.606 
4.651 




17 

18 
19 
20 
21 


5.0683 
6.3911 
8.2889 
10.163 
12.815 


26.761 
33.745 
43.765 
53.658 
' 67.660 


197.30 
156.47 
120.64 
98.401 
78.037 


.81900 
1.3024 
2.1904 
3.2926 
5.2355 


5.867 
7.398 
9.594 
11.76 
14.83 


103.0 
84.0 
66.0 
56.3 
46.8 


22 
23 
24 
25 
26 


16.152 
20.377 
25.695 
32 400 

40.868 


85.283 
107.59 
135.67 
171.07 
215.79 


61.911 

49,087 
38.918 
30.864 
24.469 


8.3208 
13.238 
21.050 
33.466 
53.235 


18.70 
23.59 
29.73 
37.50 
47.30 


39.3 

33.5 
27.4 
24.4 
19.6 


27 
28 
29 
30 
31 


51.519 
• 64.966 

81.921 
103.30 
127.27 


272.02 
343.02 
432.54 
545.39 
671.99 


19.410 
15.393 
12.207 
9.6812 
7.8573 


84.644 
134.56 
213.96 
340.25 
528.45 


59.64 
75.20 
94.82 
119.5 
147.3 


17.0 
14.4 
11.8 
10.0 

8.6 


32 
33 
34 
35 
36 


164.26 
207.08 
261.23 
329.35 
415.24 


867.27 
1093.4 
1379.3 
1738.9 
2192.5 


6.0880 
4.8290 
3.8281 
3.0363 
2.4082 


860.33 
1367.3 
2175.5 
3458.5 
5497.4 


190.1 
2.39.6 
302.3 
381.3 
480.7 


7.5 
6.3 
5.5 
4.7 
4.3 


37 

38 
39 
40 


523.76 
660.37 

83?,.48 
1049.7 


2765.5 
3486.7 
4395.5 
5542.1 


1.9093 

1.5143 

1.2012 

.9527 


87421 
13772. 
21896. 
34823. 


606.1 
764.3 
963.6 
1215. 


4.0 
3.7 
3.6 
3.0 



73 

> 
o 
O 

o 

ft 


-5 


7.79 

9.804 

12.336 


15.58 
19.54 
24.57 
30.91 

38.87 




Lbs. 

per 

1000 ft. 


128.37 

101.99 

81.06 






'0 

o 
O 

o 
'bo 

•i-H 

QQ 


tS 


7.811 
9.837 
12.39 






Lbs. 

per 

1000 ft. 


128.0 
101.85 
80.70 


64.06 
50.82 
40.32 
31.99 
25.40 





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rHOOQQO-^ Oi»«(MOOO «0 iO -^ 00 



iJrtOO-MtC 
C-OOQOC 
I M 05 OC <£ 



c-^ »-i CO <:o »« 

-"^ o t-' i-H oi 

OO-rHlAOi 

»r: ■«* CO c<i 1-1 



COCO' 
«OOC<100i 
C<I»rt »«05' 



t- c<i c<i ?o m 

CO tr-i-i»ft 00 

«ocoo<it-«o 



05C0 
t^ t-COC- 
»ft CO t-c- 
irtcvioJc^ 



t- -.^^ o -^ o 

«0 ift -«** 00 c<i 



OOO^fMQ 
CQTHC-»ft O 



OiiftWOS 



iftOift i-(QC 
-^•■^COOO^J 



c— 1-(0< 
COi«i-l( 



iOi-( c— trt ao 
05 ■»♦ »ft C<l Cvl 

1-j ?q c<i p C5 
-*!-* c<i 1-J o* od 



ir X» O 1-1 Q 

C5 p CO «c p 
t^ t-' «o »a »fl 



00«OTH-ii< 

»O&00'<* 



c<i oa c<i ca CQ 



C<IS<1C<J«00 



00 CO CO CO CO 



yj 



i4k 



Consulting this table to see how the resistance of .395 
was found for the two 500 feet leads or mains, look down 
the left hand column until we come to No. 6. The second 
column shows that the diameter of No. 6 wire is .162 mills, 
or 162-1000 of an inch. In the first section of the table 
we see that 1000 feet of No. 6 -wire has a resistance of .395 
ohms. 

Fig-. 5 shows the ordinary lighting circuit with the 
dynamo in the middle of the circuit and the lamps about 
equally distributed along the circuit. 



^Awp. ITAtnp. 2l?&Atn|», 




gg Awp. 



ZOAmpk QAwy. 



4on 



60 Ft 



7JFt 



•00 Ft 



70 rt 



50 Ft 



8Lt9. 26Lts 15 Lts 



fOLta. 22Lt». ISLt». 



T 



Figure 5 
Ordinary lighting circuit. 



Theoretically at every branch the size of the mains 
should be reduced, but, as this is practically impossible, it 
is usual to carry the large wire far enough and make a 
reduction in size only once or twice. In Fig. 5 we will 
allow a loss of two volts in the leads. Taking the left hand 
side of the circuit, if we assume the full amount of 2414 
amperes to be carried, 75 feet plus 60 feet, or 135 feet, we 
shall get a wire large enough and the drop will be less 
than the two volts rather than more. This will allow for 
some additional drop in the additional 40 feet for the last 



15 

circuit. We have then two volts equals 241/2 multiplied by 

2 

ohms, or ohms equals equals .0816 ohms. We must 

24)^ 
find a v^^ire then that has a resistance of .0816 ohms in 270 

1000 
feet. Such a v^ire will have a resistance of multi- 

270 
plied by .0816 for 1,000 feet, or .302 ohms per 1,000 feet. 
Consulting the table, we find that No. 5 wire has a resist- 
ance of .313 per 1,000 feet, and we will select this as the 
size to be used. On the right hand side of the circuit we 
will select a wire large enough to give two volts drop if all 
the current is carried to the second branch circuit, or 2 

2 
equals 25 multiplied by R, or E equals — equals .08 

25 
ohms. As the length of the wire is 170 multiplied by 2 
equals 340 feet, the resistance of 1,000 feet of this wire will 

1000 
be multiplied by .08125, or .235 ohms. 

340 • 

Consulting the table we see that No. 4 wire has a re- 
sistance of .248 per 1,000 feet, and we will»select this. For 
short branch wires it is best to use the table of the fire 
underwriters, which limits the amount of current a wire 
shall carry by the heating of the wire. Taible II shows 
these values. 



16 

Currents allowed by fire underwriters in wires of various 
sizes: 

TABLE II. 
Table A. Table B. 

Rubber Covered Wires. Weatherproof Wires. 

B. & S. G. Amperes. Amperes. 

18 3 ., 5 

16 6 8 

14 12 16 

12 17 23 

10 24 32 

8 33 40 

6 46 65 

5 : 54 77 

4 . 65 92 

3 76 110 

2 - 90 131 

1 107 156 

, 127 185 

00 150 , 220 • 

000 177 262 

0000 210 312 

For small isolated plants 5 volts drop is usually allowed 
so that the sizes for the leads we have figured for 2 volts 
drop are plenty large enough for good results for such 
plants. The drop is often expressed in per cent. A 5 per 
cent, drop is 5 per cent, of 110 volts, or 5l^ volts. 



900000000000 6i>66<!^6i^^i>^^^i> 



n ^^^^^vi 



Figure 6 ' Figure 7 

Drop in branch circtiit Drop in same circuit connected 

tapped at end. in center. 



17 

If possible, branch circuits should be tapped on to the 
mains at the center of the branch, in order to secure a 
more even voltage at the lamps. 

If the branch wires in Figs. 6 and 7 are both of the 
same size, it is easy to see that the drop in the branch wire 
as connected in Fig*. 6 is very much greater than in Fig. 7. 
In fact, the drop in Fig. 7 is only one-fourth of that in 
Fig. 6, for in Fig. 7 each branch carries half the current 
half the distance that it does in Fig. 6. Sometimes when 
from circumstances the drop in the branch circuits is bound 
to be very great, it is possible to connect them so that 
while there is a great deal of drop in each line all the lamps 
receive the same voltage. 



1 



666666666000000000 

Figure 8 

Method of connecting lamps so as to get even voltage at lamps 
even with great drop in the line. 

Fig. 8 shows such a connection. If the drop in each 
wire were five volts from one end to the other and the mains 
supplied 115 volts, each lamp would still get 110 volts. The 
great trouble with such schemes is that, although they 
work well when fully loaded, when partly loaded the volt- 
age on the lamps that do burn is excessive and certain io 
shorten the life of the lamps. The only way to install a 
plant that will be perfectly satisfactory in the way of drop 
in the lines is to use wire large enough, so that when fully 
loaded* the drop is small, then with light loads it will be 
still less. 



18 

CALCULATION OF FEEDERS FOR STREET RAILWAY 

WORK. 

In street railway wiring we have the peculiar ease that 
only one side of the line is wire and the earth is used for 
the return. 



FEEDER 
^ TROLLEY 





Figure 9 
Electric circuit of street car system. 

The rails are electrically connected to eacli other bj? 
bonding, and also are connected to the dynamo at the 
power house. It is usual to connect the dynamo to the gas 
and water pipes in the city, so as to take the current that 
naturally flows in them. In a well-bonded track there is 
not much loss of voltage in the return or ground circuit, 
and all the loss is figured in the overhead wire. The trol- 
ley wire is usually No. 1 or No. 0, so as to give mechanical 
strength. The trolle^^ wire is supplied from feeders, which 
are large wires running from the dynamos and connected to 
the trolley wires at various points. For the heaviest loads 
at least 10 per cent, loss or 50 volts is allowed in the feeder. 
HoTV large should a feeder three miles long be to carry 300 



60 , 

amperes with 50 volts loss? Here we have equals* 

300 



19 



ohms in feeder equals — . As there are three miles of feed- 

6 1 1 

er the resistance per mile ^vill be — multiplied by — 

1 6-3 

equals — , or .0555 ohms per mile. The table does 

IS 
not give the size of a wire so large as this, but it 

table does not give the size of a wire so large as this, but it 

will be ten times as large as one that has ten-eighteenths, 

or .555, ohms per mile, or a wire a little less than ten 

times as large as No. wire, is what we want. This will 

be a wire of about 105600x10 circular mils, or about 1,000,000 

circular mils, or about one inch in diameter. Such a wire 

is very expensive to put up, so that it would be cheaper to 

install four wires i^ inch in diameter, as these would have 

the same size and carrying capacity as the single large wire. 

The calculations required in wiring are almost univer- 
sally used in connection with constant potential cii*cuits. 
cults. 

There are two ways in wliich electricity is distributed: 
First, constant potential; and second, constant current. In- 




Flgure 10 
Arc light circuit. 



20 

candescent ligtiiog' and a great deal of arc lighting, street 
railway systems and all important plants for the transmis- 
sion of power are operated on the constant potential sys- 
tem. Most of the arc lights that are dn use, especially the 
older ones, are operated under the series system. In the 
first case, each lamp or motor receives the full voltage of 
the system and only part of the current. In the second, 
each lamp receives the full current flowing in the system, 
but only part of the voltage. Each arc lamp in a series 
system takes from 50 to 55 volts. 

Some of the latest arc dynamos will carry 125 or even 
150 such lamps, which requires a 'pressure of nearly 8,000 
volts. Such a voltage is very dangerous, and this is one 
reason -why the series system is not in general use. A 2,000 
candle power arc lamp requires 9 to 10 amperes, and a 1,200 
candle power from 6 to 61/2 . No. 6 B. & S. is usually used 
for 2,000 candle power arc light lines and No. 8 for 1,200 
candle power. A convenient rule by which to calculate the 
resistance of copper wire in the absence of a table is R 
equals 10.8 multiplied by length in feet divided by diameter 
in rails, or one-thousandth of an inch squared, or 

10.8 multiplied by L 
R equals ^ 



M2 

in which L equals length in feet and M equals the diameter 
in mils. 



m 



QTJESTIONS ON WIRING. 

1. What is known of the nature of electricity? 

2. Whait is known of the laws governing its action? 

3. What analogy may be used to illustrate the action 
of electricity? 

4. In the analogy of the action of water and electric- 
ity, what corresponds to electric pressure? What to elec- 
tric current? What to electric resistance? 

5. What is the unit of electric pressure? 

6. To what unit in hydraulic work does it correspond? 

7. What is the unit of electric current? 

8. What is the unit of electric resistance? 

9. What is Ohms Law? 

10. Is Ohms Law peculiar to electricity or does the 
same general la-w hold in other work? Give an example. 

11. How many volts does an ordinary storage battery 
produce? 

12. What pressure is usually employed for incan- 
descent lamps? 

13. How many amperes are used by an ordinary incan- 
descent lamp? How many by an arc light? 

14. What is the resistance of 1,000 feet of copper wire 
1-10 inch in diameter? 

15. Give an example difiCerent from that in the 
text of the loss of pressure with the transmission of fluids. 



16. On what does the loss of pressure in a pipe carry- 
ing a fluid depend? 

17. To what does the pump in a system for distribut- 
ing fluids correspond in an electric system? 

18. Give other points of analogy between the example 
you have selected and the electric system. 

19. Upon what does the loss of pressure in a wire de- 
pend? 

20. Draw a diagram of a constant potential electric 
system with four branch circuits and 38 lamps distributed 
ajnong them. 

21. What part of the wholes resistance of a circuij 
should the lamps he? 

22. What is "drop"? 

23. What is the ideal condition as regards drop in wii^ 
ing up an electrical plant? 

24. Why is it not possible to realize the ideal condition? 

25. What are calculations in wiring required for? 

26. What are the three different statements or forms 
of Ohm's law? 

27. Which is the most important in wiring problems? 

28. Write out in your own words what equation (2) 
means. 

29. How many volts are lost in a circuit carrying 120 
amperes and having a resistance of 1-30 of an ohm? 

30. What sized wire would be required for such a cir- 
cuit if it were 400 feet long? 

1 

31. How many amperes are flowing in a wire of — 



ohm if there is a drop of two volts in it? 



25 



23 



32. What is the resistance of a wire that has Syi volts 
drop when carrying 45 amperes ? 

33. If a dynamo supplies current to its circuit at 114 volts 
and each main wire has a drop of three volts, what voltage is 
there on the lamps ? 

34. A certain station fed a number of lamps at a consid- 
erable distance. The drop was 55 volts, the resistance of the 

1 

circuit was of an ohm. How many amperes was the 

220 

station carrying ? 

35. What drop is allowed in the mains of the best 
plants ? 

36. A dynamo in a basement is used to light a building. 
The wires are carried 100 feet before any branch circuits are 
taken off, and then one is taken off every 12 feet for 96 feet. 
What sized wire would be required to carry 400 amperes with 
a drop in the wires of three volts ? 

37. Why is it best to attach a branch circuit to the main 
in the middle ? 

38. A certain plant is used to light a building. It is de- 
sired to light another building 800 feet away and using 1,000 
lamps. In order to save copper, 115 volt lamps are used in 
the first building and 100 volt lamps in the second building. 
At 15 cents per pound, how much less would the copper for 
the mains cost with 100 volt lamps in the second building than 
with 110 volt lamps ? 

39. What are the objections to such a scheme as outlined 
in question 38 ? 

40. In branch circuits carrying a large number of lamps, 
what table should be employed to determine the size of 
the wire ? 



24 

41. Haw many volts drop are usually allowed in the 
feed wires of street railway circuits? 

42. How do the currents return from the street cars 
to the dynamo? 

43. Why does such a return as is used ' in street 
railway work save copper? 

44. How large a wire would be required to carry 500 
amperes 1^^ miles with a drop of 75 volts? 

45. Wha-t would such a wire cost at .14i/$ per pound? 

46. If 125 volts drop were used, what current would 
this wire carry? 

47. If 500 amperes were carried on a wire at 125 volts 
loss IVo miles, how much would the wire cost at .141^ per 
pound ? 

48. What size of trolley wire is usually employed in 
street railway work? 

49. Sketch out a system of wiring for street railway 
circuit hy which the voltage when near the power house is 
less than when at a distance from it. 

50. In what two ways is electricity distributed? 

51. For what is the series system used? 

52. What is the characteristic feature of the constant 
potential system? 

53. Of the series system? 

54. What current is required for a 2,000 c. p. arc lamp? 

55. What current is required for a 1,200 c. p. arc lamp? 

56. What is a convenient rule for calculating the re- 
sistance of a copper wire in the absence of tables? 



CHAPTER IL 

ELECTRIC BATTERIES. 

m the year 1786 Galvani was making- some experiments 
with frogs' legs and had a number supported by the spinal 
cord from copper hoops attached to an iron railing. He 
noticed that when the muscles touched the railing that the 
frog's legs contracted spasmodically. This experiment led 
finall3' to the production of the electric battery. 

Volta, in the year 1800, produced the so-called voltaic 
pile, which is one of the simpler forms of a battery. The 
easiest and most simple way to make a battery is to insert 
in a jar partially filled with acidulated water, or even brine, 
a strip of zinc and one of copper. Upon joining the zinc 
and copper outside the solution by a metallic conductor, a 
current of electricity will flow from the copper to the zinc 
through the conductor and from the zinc to the copper 
through the acid. The way in which the current flows 
through the acid is not thoroughly understood, but this 
flow is accompanied by the oxidation or slow laming of the 
zinc and "by the evolution of hydrogen gas on the copper. 
The primary cause of the flow of the current is the com- 
bustion or oxidation of the zinc, and if the conditions are 
properly arranged the amount of current that flows is 
strictly proportional to the amount of zinc consumed. 

The appearance of the hydrogen gas on the copper re- 
duces the current which flows by covering it to a great ex- 
tent with a thin layer or coating of hydrogen gas. The 
battery will deliver much more current when means are 
provided to prevent the formation of gas upon the copper. 



26 
TABLE in. 

ELECTRO-CITEIVIICAL SERIES OF THE ELEMENTS. 



— 




+ 


Oxygen 




Caesium 


Sulphur 




Potassium 


Nitrogen 




Sodium 


Flourine 




Zinc 


Chlorine 




Iron 


Bromine 


Copper 


Iodine 


Silver 


Phosphorus 


Mercury 




Carbon 


Platinum 




Antimony 


Gold 





Hydrogen 

The process of coating the copper with hydrogen gas 
is called polarization. The zinc plate is called the positive 
element, the copper plate is called the negative element. 
The binding post by vrhich the current leaves the copper 
is called the positive pole, because the current flov^s from 
this binding post through the outside circuit to the nega- 
tive pole on the zinc plate. Some metals may be used in 
place of the zinc as the positive element in the battery; 
among these the more important are potassium and sodium. 
Many medals may be used to take the place of copper, but 
the material most frequently employed is carbon. 

A battery composed of zinc arid carbon has a much 
higher electro-motive force than one in which the zinc and 
copper are used; in fact, the elements may be arranged in a 
series in which any one may be used as a positive element 



27 

in combination witli any below it, and as a negative ele- 
ment when used in combination with any above it. Table 
No. 3 is such a list. 

Zinc and copper in a solution of sulphuric acid give an 
elctro-motive force of about one volt. Zinc and carbon 
ffive about two volts. Zinc and carbon with an alkaline 
solution, such as salamoniac or potash, give about one volt 
and one half. Various means are employed to prevent the 
hydrogen from appearing or adhering to the negative ele- 
ment. Some of these are mechanical, such as the use of 
very fine metallic powder, such as platinum sponge, which 
permits the bubbles of gas to escape when very small, or 
by the use of a stream of air bubbles which mechanically 
carries away the hydrogen from the surface of the negative 
element. The first method is used in the Smee battery, in 
which the nej>"ative element is a thin plate of silver on 
which has been deposited a coating of very finely divided 
metallic platinum called platinum sponge. 

By all means the more important method for preventing 
the appearance of hydrogen on the negative element is t3ie 
use of some chemical which consumes the hydrogen before 
it reaches the negative element. This is usually accom- 
plished by inserting the negative element in a porous cup 
which is filled with a powerful acid or with some other ma- 
terial which burns up the hydrogen. 

When the zinc of a battery is consumed it combines 
with oxygen from the solution in which it is placed, and for 
every atom of oxygen which chemically unites v^ith the 
zinc two atoms of hydrogen are evolved, and these travel 
from the surface of the zinc through the solution in some 
wav toward the negative plate. If somewhere between 



28 

the positive and negative plates a porous cup is placed, the 
hydrogen will pass through the pores of this cup on its way 
toward the negative plate. 

If within the porous cup is placed a very powerful acid, 
the hydrogen is consumed or burned up as soon as it reaches 
this acid, and thus the polarization which would otherwise 
occur from the appearance of hydrogen gas on the negative 
plate is prevented. 

Zinc is used as the positive element in almost every 
battery. 

The reason wh}^ primary batteries are not used for the 
purpose of developing power is not that they could not be 
so used, but because the zinc and sulphuric acid which 
would be required to produce the power are so expensive as 
to be prohibitive. Efforts are being constantly made to 
produce a battery in which carbon may be used as the posi- 
tive element. If such a battery could be commercially pro- 
duced with an efficiency equal to the zinc battery, it would 
revolutionize the present methods of producing power and 
be one of the greatest inventions. 

If a plate of carbon be immersed in fused nitrate of soda 
and an iron plate be used as the negative element, current 
will be obtained. There is a dispute as to the source of 
this current, some claiming that it is electro-chemical and 
others that it is produced by electro-thermaH effects. In 
either case the battery has not been sufficiently effective 
to be practical. 

A very powerful battery for experiment«al purposes (see 
Fig. 11) may be constructed by using a number of oarbon 
brushes or plates' fastened parallel to and close to each side 



29 



of the zinc plates and arranged so as to be plunged into a 
solution of sulphuric acid, water and bi-chromate of pot- 
ash. 




Figure 11 
Dip or plunge "battery. 



This solution may be made by adding to one quart of 
water one-half pint of commercial sulphuric acid and one- 
quarter pound of bi-chromate of potash. 

The writer has obtained a current of 30 amperes from 
a single cell of this battery, six inches in diameter and six 
inches deep. It is necessary to provide means by which 
the plates may be raised from the solution as soon as the 
occasion for their use is past. 

In order to get the best results from the use of the zinc 
plate when made of commercial zinc, it is necessary to 
amalgamate it or wet the surface with liquid mercury. 
This may be easily done by first mechanically cleaning the 
plate, next removing any grease by the use of potash or 



30 



scda, and third by immersing it for a few moments in an 
acid. The acid which is intended to be used as an electro- 
lite for the battery will answer. This will cause the zinc 
plate to present a perfectly clean surface, and the mercury 
will quickly spread all over it. This treatment prevents the 
acid from attacking the zinc when the outside circuit is not 
closed. 

Below is a table giving the names of a number of the 
more prominent cells m use, and the voltage on an 
open circuit, the electrolite used and the character of the 
plates. 

TABLE IV. 
DATA OF COMMON BATTERIES. 



Name of Cell. 


E.M.F. 


Plates. 


Electrolite. 


Bunsen 


1.95 

1.93 

1.07 

1.47 
1.50 

.90 
2.00 


Zinc 
<• 

a 

Lead 


Carbon 

Copper 

Carbon 

Copper Oxide 


r Nitric and 
t Sulphuric Acid 
1 Nitric and 
I Sulphuric Acid 
( Copper Sulphate 
t Zinc Sulphate 

Salamoniac 
Salamoniac Paste 


Groove 


Gravity 


Leclanche 

Dry Cell 


Edison Lelande 

Lead Storage 


Caustic Potash 
Sulphuric Acid 



It is a fact that with perfectly pure zinc and all condi- 
tions being perfect, the passage of a certain amount of 
current through a battery is invariably accompanied by the 
solution or consumption of a certain amount of zinc. 

Conversely, if a current from an outside source be passed 
through a battery from the zinc through the 



31 

electrolite to the carbon, metallic zinc will be deposited 
from the solution, provided the battery has been used 
before the experiment is made. 

In fact, the amount of electricity which passes through 
a properly arranged solution may be very accurately meas- 
ured by the amount of metal which is deposited from the 
solution. An instrument arranged to measure current in 
this way is called a volta-meter. 

Practical electricians will recall the old Edison meters, 
by which current was measured and sold to customers from 
the old Edison stations. 

In this instrument the current was caused to pass from 
one plate of zinc through a solution of sulphate of zinc 
and out through a second plate of zinc. The passage of ten 
amperes for ten hours through this meter causes the solu- 
tion of 4.33 ounces of zinc from the first plate by which the 
current enters the solution, and the deposit of an exactly 
equal amount from the solution upon the second plate. 
Every month these two plates were removed and weighed 
and the weight compared with what it was a month before. 
The amount of current that had passed was calculated 
from the change in weight. The plate \ 
which the current enters the solution is called 
the anode, and the plate by which the current leaves 
the solution is called the cathode. It will be convenient to 
remember that the current always carries the metal with it 
from the anode into the solution and from the solution on 
to the cathode. In fact, it is easy to determine the direction 
in which a current is flowing by causing all or a part of 
the current to pass through a glass tumbler partly filled 
with a solution of sulphate of copper or blue vitriol, in 



32 

which are immersed a couple of nails, one connected with 
each side of the circuit which is to be tested. On one of 
the nails will appear bubbles of gas, while the other will be 
more or less rapidly covered with a layer of metallic copper. 
The current will How from the first nail through the solu- 
tion to the second nail. 

A very great deal of attention is now being given to the 
chemical changes that are brought about by the ac- 
tion of electric current upon the various chemical com- 
pounds, and it is the writer's belief that the greatest ad- 
vances in electrical knowledge during the next few years 
will be made along this line. 

ELECTRO-PLATING. 

We have discussed above the principles upon which elec- 
tro-plating depend. 

The general scheme is to cover one mfetal with a thin 
layer of another metal by electro-chemical means. To do 
this a solution is prepared and in this solution are immersed 
a number of aaiodes, usually of nickel, silver, copper, gold or 
brass, with which it is desired tc plate the second metal. 
In the same solution is immersed the metal to be plated. 

A current is passed from the anode through the solu- 
tion to the metal to be plated, or cathode. The action of 
the current is to decompose the solution and deposit the 
metal from the solution on the cathode, at ihe same time 
forming a portion of acid which in some way passes through 
the solution to the anode and there dissolves just as much 
of the anode into the solution as was deposited by the cur- 
rent out of the solution. 



33 

The amount of metal deposited upon the cathode de- 
pends upn the amount of current which flows and upon 
the time it flows or upon the ampere hours of current. If 
the amount of current is properly arranged, the metal will 
be deposited from the solution in an even adhesive layer. 
If too much current flows, the metal will not be deposited 
in such a flrm layer and the corners will have a blackened 
appearance, when the work is said to be burned. The skill 
of the plater comes, first, in getting the work to be plated 
chemically clean; second, in arranging the solutions prop- 
erly; third, in adjusting the lamount of current to the so- 
lution and the amount of w^ork. One kind of solution is 
used with zinc, another ^^ith nickel, another with silver, 
and another wiih copper. 

Each solution requires special treatment, and to get 
good results, expert knowledge. 

It is a peculiar fact that a mixture of metals, such as 
brass, may be used in plating, but thiat the voltage required 
with such a solution is two or three times higher than that 
required by copper or nickel. 

Below will be found a table of the elements, giving their 
names, atomic weights, relative resistances by volume, rela- 
tive resistance by weight and weight deposited by ten am- 
peres in ten hours. 



34 



TABLE V. 



PROPERTIES OF METALS 







a: 


(V 










£ -c 


o 




-c 




>> 


n § 


-»-3 






.i-H 


^ o 


CO 3 


(~> 


znJH 




. g 

o 


w P bC 


1^ 


5C 


Depo 
J ours 
peres 








£^ 


o 






"o 




u 


^z< 




P. 




s 


S -^ r-i 
O ^ t* 




8.94 
10.5 
19.26 


e^c^S^ 


P^o 


< 


S.S^ 


Copper 


1.00 
1.113 

2.203 


1.06 
1.00 
1.27 


63.4 
108. 
197. 


.2636 


Silver 


.8980 


Gold 


.5460 


Aluminum 


2.56 
7.13 
21.5 

7.84 
8.82 
7.30 
11.4 
8.5 
6.72 


.526 

2.732 

13.62 

5.33 

7.69 

6.75 

15.55 

12.16 

16.69 


1.95 

3.74 

6.02 

6.46 

8.28 

8.78 

13.05 

13.92 

23.60 


27. 

65.2 
197. 

56. 

58.8 
118. 
207. 

122. 


.0569 


Zinc 


.2710 


Platinum 


.4145 


Iron 


.0776 


Nickel 


.1222 


Tin 


.2453 


Lead 


.4303 


German Silver 




Antimony 


.1863 


Manganese Steel 


7.8 
13.6 

9.8 


34.82 
89.76 
89.92 


42.43 
62.73 

87.23 


200. 
210. 




Mercury 


.8315 


Bismuth 


.3492 



STORAGE BATTERIES. 

When two plates of lead are immersed in a solution of 
sulphuric acid and a current is passed through the cell, 
there is a tendency to produce an oxide of lead on one plate 
and spongy or metallic lead on the other plate. If the 
plates are properly prepared and the current is sent 
through the battery repeatedly, first in one direction and 
then in the other, the cell will finally be completed or 
formed. This method of making a storage cell is called 
the Platite process. 

In a completed storage battery, passing the current 
through the battery is called charging it, and the charging 
produces chemical changes on the plates, which will pro- 
duce electric currents if the plates are connected by a wire 
outside the battery. 

When current is flowing from the battery it is said to 
be discharging. The battery will continue to discharge un- 
til the chemical products formed by the charging current 
have been reduced to their original state. The advantages 
possessed by the storage battery over the primary battery 
are that there is no polarization and the resistance of the 
battery may be made very much lower than that of a pri- 
mary battery. 

As its name indicates, the storage battery is practically 
a device for absorbing energy from an electric circuit at 
one time and restoring it to the electric circuit at some 
subsequent time. The charging current in a good battery 
may vary between wide limits, but the best results will be 
obtained from a moderately small amount of charging cur- 
rent. The same thing is true of the amount of the current 



Ji 



36 

during discharge. The best modern storage batteries use6 
for horseless carriage work, where extreme lightness is es- 
sential, have a capacity of two ampere hours per battery 
for every pound of weight in the battery and a capacity of 
four watt hours per pound in the battery. 

The two principal uses for storage batteries at the pres- 
ent time are for storing power in central stations during 
times of light Joad, so that it can deliver the power during 
the time of the heaviest load, and second, for furnishing 
electric current for motors for horseless carriages and elec- 
tric launches. Storage batteries may also be used to great 
advantage near the end of a long line which has an inter- 
mittent load on it. The battery will absorb current during 
times of light load and deliver it during times of heavy load, 
thus making the current that comes over the line from the 
central station practically constant. The great objections 
to the storage battery are its cost and weight. So far. no 
one has succeeded in making a practical battery out of any 
other material than lead. 



QUESTIONS ON CHAPTER 11. 



BATTERIES. 



1. What two men were chiefly instrumental in the early 
development of the electric battery? 

2. Describe a way in which a simple battery may be 
constructed, 

3. In which way does the current from a battery flow 
in the outside circuit? 

4. What; is the real cause of the flow of <>urreiit in a 
battery? 

5. What is polarization? 

6. What is the positive element in a battery? What is 
the negative element? 

7. What is the positive pole of a battery? 

8. What metals may be used to advantag-e in place of 
copper in a battery? 

9. Consulting table No. 2, why is it that zinc and car- 
bon produce a higher E. M. F. than zinc and capper? 

10. What means are used to prevent hydrogen from aj)- 
pearing on the negative element? 



38 

11. Describe a chemical means for preventing* hydrogen 
from appearing on a negative element? 

12. Why are primary 'batteries not used to develop 
power? 

13. Describe a battery in which carbon is used as a 
positive element. 

14. How may a powerful battery for experimental pur- 
poses be made? 

15. In order to get the best results from a zinc plate 
when used in a battery, how must it be treated? 

16. What is the relation* between the amount of zinc 
consumed in a battery and the amount of current it pro- 
duces? 

17. What is a voltameter? 

18. Describe the Edison current recording meter. 

19. What is an anode? What is a cathode? 

20. Does a current of electricity carry a metal with it 
or against it? 

21. How may the direction of a current be determined 
by chemical means? 



ELECTRO-PLATING. 

1. What is accomplished by electro-plating? 

2. Describe the process of electro-plating. 

3. On what does the amount of metal deposited depend? 



39 

4. What is the effect of having too much current in 
electro-plating? 

5. lb it possible to plate with an alloy, such as brass? 
If so, how? 



STORAGE BATTERIES. 

1. What is a storage battery? 

2. Describe the process of charge and discharge. 

3. What advantages does the storage battery possess 
over ordinary batteries? 

4w For what are storage batteries usea/ 



y. 



CHAPTER m. 



MAGNETISM. 



If a hard piece of steel be brought into contact with a 
mag^net it will become magnetized and will retain more or 
less of the magnetism. If steel of the proper kind and 
which has had the proper treatment is chosen, the mag- 
netism will be constant, almost absolutely constant. Tung- 
sten steel, artificially aged, is used for volt meters and 
measuring instruments in which the accuracy of the instru- 
ment depends on the constancy of the magnetism of the 
steel, and the steel meets the requirements. If a magnet 
is supported so as to be free to turn in a horizontal plane, 
it will set itself north and south, as is seen in the mariner's 
compass. 

The pole that turns toward the north is called the 
north or N. pole and the other the south or S. pole. It is a 
fact that like poles repel each other and unlike poles at- 
tract each other. 

The earth on which we live is a great mag-net, and this 
has its S. magnetic pole at or near the north geographical 
pole, for if by definition a N. pole is one that points to the 
north and unlike poles attract each other, the N. pole of the 
compass must point toward the S. magnetic pole of the 
earth. 



41 






A magnet is surrounded by what is called a field of 
force. 

What are called lines of force are supposed to springs 
from the iron or steel at the north pole, pass through the 
air to the south pole, enter the iron and pass through it to 
the north pole. The lines of force are said to flow in the 
direction indicated. This should be carefully kept in mind, 
as it will be . used a great deal later. 

A line of force is always 
a closed curve, and if any 
one travels along the whole ^*.--v,----, 

of a line of force one will al- 
ways come to the -starting 
point. A line of force is the 
direction of the magnetic 
force at any point. 

The lines of force from 
the earth are flowing in the 
air from the south to the 
north. Near the equator the 
magnetic force acting on a 
horizontal compass needle is 
greater than in other parts 
of the earth. 

The earth as a magnet acts on a horizontal compass in 
the United States with a force corresponding to from one 
to two magnetic lines per square inch. 

If a bar raagnet be placed under a piece* of 
pasteboard or glass, and iron filings be sprinkled over the 
pasteboard or glass, they will arrange themselves along 










Figure 13 
Bar magnet and field of force. 



42 



the lines of force. A picture of the mag-netic lines produced 
in this way is called a magnetic spectrum. 

A bar magrnet bent iniio a TT shape is called a horse-shoe 
magnet, and it is interesting -to get the magnetic spectrum 
of such a magnet. (See Fig. 20.) The region of powerful 
influence is smaller than with a bar magnet, but much more 
intense. The spectrum of two horse-shoe magnets attract- 
ing aind repelling each other is very instructive* 

A wire carrj/ing a current has a 
very peculiar si^ectrum. This spec- 
trum consists of concentric circles, 
denser near the wire than at a dis- 
tance form it, as indicated in the 
sketch. 

When the direction of the cur- 
renit is reversed, the direction of the 
lines is reversed. It is possible to find 
the direction of a current in a wire 
by the use of a compass by deter- 
mining in what direction the concentric mag- 
netic lines or magnetic whirl flows. A free north pole 
w^ould move in the direction in which the magnetic lines 
flow, or would revolve around the wire. . It is not possible, 
of course, to obtain a free north pole or a north pole with- 
out a south pole, so that all that can practically be discov- 
ered is the direction in which the north pole of a compass 
is moved. The direction in which the north pole is moved 
is the direction of the whirl, and the direction, of the whirl 
bears the same relation to that of the current that 
the direction of rotation of a screw bears to its motion 
back and forth. 




Figure 14 

Magnetic spectum of wire 
carrying current. 




43 

If the north pole of a compass moves in a rig-ht hand 
direction, it shows that the lines of force flow right hand- 
ed and that the current is flowing away from the observer. 

If the north pole of a compass is moved to the right 

when placed over a wire 

carrying current, it 

shows that the whirl is right _ 

handed and the current is 

flowing away from the ob- ^, 

^ -^ Figure 15 

server. Direction of current indicated by 

motion of compass needle 
If, on the other hand, placed under a wire 

^ ,, . - ^ - carrying current, 

it moves to the right when 

placed under the wire, it 

shows that the whirl is left handed and that current is trav- 
eling toward the observer. 

It is a fact that when current is caused 
to circulate around an iron or steel core, the core 
becomes magnetized, and if the current is strong Enough 
the core becomes much more strongly magnetized than is 
possible with permanent magnets. It is easy to get a 
magnet of such strength that the armature is attracted with 
a force of 125 pounds per square inch, and in extreme cases 
the magnetism of a piece of soft iron has been pushed to 
such an extent as to produce a magnetic pressure of 1,000 
pounds per square inch. A piece of soft iron surrounded 
with such a circulating current becomes a powerful electro- 
magnet, but almost all the magnetism disappears when the 
current is withdrawn. 

There Ls a relation between the polarity of an electro- 
magnet and the direction in which the current circulates 
around the magnet core. When the current circulates 



44 




arouDd the magnet in 'the direction of the motion of the 
hands of a watch, the pole facing 
the observer in a S. pole. 

A little thought will show 
that the magnetism of an elec- 
tro-magnet may be regarded as 
the sum of the magnetic whirls of 
the wires surrounding the core. 
An inspection of Fig. 17 will 
show this. 

A helix is a coil of wire carrying a 
^;^--r-r>--V2fr:^ current; the name is usually applied 
; ^@' (^r i^ *^j t^))y only to a single long spiral of wire. 

piece of iron placed in a helix carry- 
current becomes an electro-magnet. 
A helix carrying current has all the 
properties of an electro-magnet, but 
the magnetic properties are not so pow- 
erful. 



Figure 16 
Relation between polarity of 
electric magnet and direc- 
tion oi exciting current. 



^^^^^^^ A pi 

Figure 17 
Showing that the mag- 
netic lines of a helix or 
electromagnet are due to 
the addition of the mag- 
netic whirls of the wires 
carrying the exciting 
current. 



in an acid solution, 
copper are connected with a helix. 
This helix will turn and point north 
and south in the same way a com- 
pass would. It is attracted or re- 
pelled by a permanent magnet in 
the same way that a compass is. If 
there were two of them floating in 
the same vat they would arrange 
themselves end to end with N. and 
S. poles adjacent. 



Fig. 18 shows a zinc and copper 
plate attached to a cork and floating 
The zinc and 




Figure 18 

Floating helix and 

electromagnet. 



45 

If now a piece of soft iron be placed in the helix all 
the above actions become much stronger, but this is the 
only difference. A piece of hard steel may be made into a 
permanent magnet by being inserted into a helix carrying 
current. A helix with a large number of turns is called a 

solenoid. 

A very important relation exists between a w^ire carry- 
ing a current and a magnetic field. A magnetic field is a 
space through w;iich the mangetic lines travel. 




Figure 19 . 
Magnetic spectrum of a helix ; compare with spectrum 
of bar magnet. 




^^, 



Figure 20 

Wire carrying current in a magnetic field tending to move 

in or out of the magnet- 



46 



Fig". 20 shows a liorse-shoe magnet and in such a mag- 
net the most powerful field exists betw^een the ends. Fig. 
20 also shows a wire placed in this field and at right angles 
to the plane of the magnet. If, now, current be sent 
through this wire, it will experience a mechanical force 
tending t« move it sideways across the lines of force, either 
into or out of the magnet. 




Figure 21 



Fig. 21 shows a method by which a wire carrying a cuiv 
rent and free to move may be arranged. This is a most 
important experiment, and, if possible, should be performed 
by every one interested in the study of electricity. The 
experiment shown in Fig. 21 is the fundamental experiment 
showing why it is that a motor will operate. By reversing 
the experiment shown in Fig. 21, and by causing the wire 
to move across the lines of force, it is possible to generate 
current in the wire. This Is a fundamental experiment, for 
it shows in the simplest possible manner how mechanical 
power can be transformed into electrical power, or how a 
dynamo works. The relations that exist between the direc- 



47 



tion of motion of the wire, the direction of lines of force 
and the direction of the current in the wire when moved by- 
hand or by mechanical force, is most easily remembered 
bv extending the thumb, first and second finger of 




Figure 22 
Rotation of direction of lines, motion and current illustrated. 

• 

the right hand at right angles to each other. When so ex- 
tended the thumb points in the direction of the motion, the 
first finger points in the direction of the magnetic lines, a^d 
the second finger in the direction of the resulting current. 
The rule for remembering the direction of motion, lines 
and current when the wire is supplied with a current from 



48 



a battery or other source Is the same as the case of a wire 
moved by mechanical force, given above, except that the 
thumb, first and second fingers of the left hand are used 
instead of the right. 



DmeCTfON OF 




Figure 23 
JpToduction of E. M. F. by moving wire in magnetic field. 




' Figure 24 

Passage of current through a loop in a motor 
and resulting motion. 

Fig. 24 shows an electric motor in which the rules 
given above may be applied. In Fig. 24 the N. pole is 
shown at the top and consequently the .magnetic lines flow 
downwards, across the upper air gap and through the ar- 



49 



mature iron and across the lower air gap. If, now, cur- 
rent flows from some external source through the loop 
from A to B, the wire iai the upper gap will be forced to 
the left. 

As the current in the other side of the loop will be flow- 
ing in the opposite direction to that in the upper side, this 
part of the loop will be forced to the right; thus the wire 
in "Ehe upper air gap and the wire in the lower gap both 
tend to rotate in a direction opposite to that of the hands 
of a watch. Since the direction of the current in all the 
wires in the upper air gap in an actual armature is the same, 
each of these wires will be forced to the left and in a similar 
manner each of the wires in the lower air gap will be forced 
to the right. The sum of the mechanical forces acting on 
the wires in the upper and lower air gaps is the torque or 
twisting effort of the armature. The mechanical force de- 
pends on two things, viz: the number of magnetic lines flow- 
ing across the air gap and the current flowing in each wire. 
When a wire one foot long is in a field of an intensity of 
100,000 lines per square inch, there will be a mechanical 
force of ,106 pounds or 1.7 ounces pushing the wire sideways 
for every ampere of current flowing in the wire. It is clear 
now why it is so necessary to fasten the wires to the arma- 
ture by'bands, for it is not the iron which tends to move, 
but the wire on the outside of the iron, and in order to 
communicate the torque from the wire to the iron some 
such means are necessary. 

Fig. 25 shows the same machine as Fig. 24, except that 
the armature is driven in the opposite direction by me- 
chanical power. We have the north pole at the top and 
the current tending to flow through the wire in the same 
direction as in Fig. 24. There will be a drag on each wire 



50 



proiportional to the number of lines which flow across the 
upper air gap through the armature and across the lower 
air gap, and also proportional to the current which is flow- 
ing in each wire. 




Figure 25 

Motion of a wire i*i a magnetic field and the 
resulting current. 

Since there is the same mechanical drag in each wire 
in the upper air gap and an equal mechanical drag in the 
opposite direction in each wire in the lower air gap, it re- 
quires a mechanical torque or twisting effort on the arma- 
ture to force the wires carrying the current through the 
air gaps. It sometimes happens that when very excessive 
currents pass through the wires on an armature the me- 
chanical drag is such that the wires slip over the surface 
of the iron, usually cutting through the insulation at some 
point and burning out the armature. This is one advantage 
of the modern tunnel wound armature, for its construction 
gives an almost perfect mechanical support to the armature 
wires. When a wire moves so as to cut 100,000,000 lines of 
force per second, there is produced in this wire an electro- 
motive force of one volt. It will pay the student to per- 
form the experiments illustrated in this chapter, as he can 
in this way gain a first-hand knowledge of the fundamental 
principles upon which the operation of motors and dynamos 
depend which can be secured in no other way. 



QUESTIONS ON CHAPTER III. 

1. What happens if a hard piece of steel is brougiit 
eontact with a magnet? 

2. What is a mariner's compass? 

3. What is the north pole? The south pole? 

4. What is a field of force? 

5. In what direction do magnetic lines flow? 

6. What is a magnetic spectrum? 

7. What is peculiar in the magnetic spectrum of a 
horse-shoe magnet? 

8. Describe the magnetic spectrum of a wire carrying 
a current. 

9. What is a magnetic whirl? 

10. What is the relation between the direction of flow 
of current in a wire and the direction of the magnetic whirl? 

i J * 

11. If the current in a vertical wire moves the north 

pole of a compass to the right when the compass is held 
between the wire and the observer, in what direction does 
the current flow? 

12. A wire running north and south causes the north 
pole of a compass placed over it to be deflected toward the 
west; which way is the current flowing in the wire? 

13. A lineman wished to learn the direction of the 
current in a wire over his head and observed that the com- 



52 

pass needle when held over the wire face down was deflected 
toward the east, the wire running north and south. In what 
direction does the current flow in the wire? 

14. What is an electro-magnet? 

15. What is the difference between a permanent mag- 
net and an electro-magnet? 

16. What is the relation between the polarity of aai elec- 
tro-magnet and the direction in which the current circu- 
lates around the iron core? 

17. Is there any relation between the polarity of an 
electro-magnet and the magnetic whirls in the wires of 
which it is composed? If so, what? 

18. What is a helix? What are its properties? 

19. What is flie difference between a helix and an 
electro-magnet? 

20. When a wire carrying a current is placed in the 
field of a horse-shoe magnet, what occurs? 

21. Explain the action of the mechanism in Fig. 20 
when it operates as a motor. 

22. Explain its action when it operates as a dynamo. 

23. What is the relation between the direction of the 
motion, direction of the lines and the direction of the cur- 
rent when the apparatus is used as a dynamo? 

24. What is the relation between the direction of the 
motion, the direction of the lines of force and the direction 
of the current when the apparatus is being used as a motor? 

25. Why will the armature in Fig. 21 reverse its direc- 
tion of motion if the north pole were placed at the bottom 
instead of at the top? 



53 

26. Why is it that both wires in the loop in Fig. 21 ten3 

to rotate the armature in the same direction? 

• 

27. We have seen that the earth is a great magnet, with 
its south magnetic pole near its north geographical pole. 
If a person is riding a biciycle toward the west, in what 
direction will the E. M. F. be generated in the vertical 
spokes in the moving wheel? 

28. If a current is traveling in a coil of wire that is free 
to move, and the coil turns so that its plane is east and 
west, in what direction will a current be flowing in this 
coil? 

29. Two men standing in an east and west line, 50 feet 
apart, raise a steel tape from the ground. In what direction 
does the current tend to flow along the steel tape? 

30. In an Edison motor the armature is revolving right- 
handed as seen by the observer. If the pole on the left is a 
north pole, in which direction does the current flow in the 
wires under the north pole? 

31. When a wire is in a field of 100,000 lines per square 
inch, what is the mechanical force acting on the wire per 
ampere per foot? 

32. How many magnetic lines must be cut per second 
to produce one volt? 

33. Is there any other reason for banding down arma* 
ture wires to the core except to prevent the action of centri- 
fugal force? 



/ 



CHAPTER IV. 



THE MAG^^ETIC CIRCUIT. 



De La Rives' floating battery (Fig. 18) showed that a 
helix canying a current is a magnet. If the current is 
measured and the number of turns counted, it will be found 
that the strength of a given helix depends on the number 
of amperes of current that flow through it, and if a con- 
stant current is used the strength of the helix depends on 
the number of turns. 

Putting these two facts together, we see that ihe 
strength of any helix is proportional to the product of the 
number of turns times the number of amperes or the am- 
pere turns. The number of ampere turns is a measure of 
the magnetizing force. 'By producing the magnetic spec- 
trum of a helix (Fig. 19) it will be seen that all the lines 
traverse the center of the helix and return through the space 
outside of the helix. If the diameter of the helix is large, 
more lines will flow through it than if it is small. If it is 
short, more lines will flow through it, other things being 
equal, than if.it is long. A careful consideration of these 
experiments will show that there is the same relation be- 
tween the number of lines of force and the magnetizing 
force or number of ampere turns and the magnetic resist- 
ance that there is between the current, voltage and resist- 
ance in the electric circuit. If we allow N to represent the 
number of lines of force produced, A T to represent the 



55 

number of ampere turns, and M R to represent the mag- 
netic resistance or reluctance, we have N equals A-T divid- 

A T 
ed by M Jl, or . It will be noticed at once that this is 

M R 

Ohm's law transferred to the magnetic circuit. 

The magnetic resistance is proportional to .the length of 
the magnetic circuit and is inversely proportiomal to the 

1 
area of MR equals — , where 1 is the length of the magnetic 
A 

circuit and A equals the area. Substituting this in the for- 
mula we have 

A 
N equals A-T multiplied by — 

1 

If A and L be expressed in inch measurements, we have 

A-T multiplied by A 

X equals (4) 

1 multiplied by .3132 

We will now see what effect the introduc- 
tion of iron into the helix wili have. Figs. 18 and 19 show 
that current flowing in a helix produces lines of force in 
the helix and causes it to become a weak magnet. If a 
piece of soft iron be inserted in the helix, the iron becomes 
very strongly magnetized. 

It can be shown that a great many more magnetic lines 
of force traverse the helix when it has the ircm inside than 
before. Therefore the iron offers an easier path for the 
magnetic liues than the air did because more lines flow 
under the same circumstances when the helix is filled with 
iron than when the iron is absent. Under some circum^ 



m 

stances the iron will -transmit or allow to pass 3,000 times 
as many lines as the air 

The presence of the iron multiplies the numDer of mag- 
netic lines by offering an easier path for the flow of the 
lines. If it was not for this multiplying action of the iron, 
dynamo electric machinery would be impossible. That 
property of iron, in virtue of which it conducts magnetic 
lines, is called permeability. 

Now the permeability of iron is not constant. When 
ftnly a few lines are flowing in a piece of iron the perme- 
ability or multiplying power is greatest. If the iron is al- 
ready carrying a large number of lines the permeability 
will be small. 

The capacity of the iron for carrying lines may be com- 
pared to the capacity of a sponge for soaking up water. 

When the sponge has only a little water in it, it will 
readily absorb more, but when the sponge has taken up 
nearly as much water as it will, or is saturated, it will ab- 
sorb more water only with reluctance. When iron is car- 
rying about as much magnetism or as many magnetic lines 
as it will, it is said to be saturated. The permeability of 
iron at various numbers of lines per square inch in the iron 
or at various degrees of saturation has been measured, and 
the results obtained are shown in the following table: 



5« 



^ 



I'ABLE VI. 



TABLE OF PERMEABILITY 



WROUGHT IRON 




CAST IRON 




o 




< 


t-i 


o 




<5 


u 


k: 


^S|c 


J=! 

•iH 


^^^A 


s: 


rmeab 
Multi 

gPow 
Iron 


el 








S 
fl 


Ampe 
Turns 
Inchi 
Lengt 


II 




Ampe 

Turns 

j Inch i 

Lengt 


ss 




3 


h5cq 




5 


30,000 


3,060 


9.8 


3.06 


25,000 


833 


300 


9.4 


<^,000 


2,780 


14.4 


4.72 


30,000 


580 


51.7 


10.2 


50.000 


2,488 


20.1 


6.29 


35,000 


390 


89.7 


27.5 


60,000 


2,175 


28.0 


8.76 


40,000 


245 


163. 


51. 


65,000 


1980 


32.8 


10.26 


45.000 


135 


333. 


104. 


70,000 


1,920 


40.7 


12.7 


50,000 


110 


454, 


142. 


75,000 


1,500 


50.0 


15.6 


60,000 


66 


90y. 


284. 


80,000 


1,260 


63.5 


19.8 


70,000 


40 


1750. 


548. 


85.000 


1,030 
830 


82.5 
108.0 


25.8 
33.8 










90,000 










95,000 


610 


156. 


48 8 










100,000 


420 


238. 


74.5 










105,000 


280 


375. 


117. 










110,000 


175 


629. 


197. 










115,000 


95 


1210. 


378. 










120.000 


60 


2000. 


626. 










125,000 


40 


3125. 


978. 










130,000 


30 


4333. 


1356. 










135,000 


24 


5626. 


1761, 


* 








140,000 


18 


7777. 


2434. 











^ 



68 



;«060Cf}t4 



iDOOoa 



60OOO 



«0000 




40000 



Coooc 



1600 



B. H. Cnrve 

Curves showing the same relations graphically that the 
table gives numerically. 

This table vras calculated by measuring the number of 
magnetic lines flowing through an iron ring surrounded 
by a certain number of turns of wire (see Fig. 27) and 
comparing this with the number that would flow through 
the air when a wire coil of the same size, carrying the sama 
current, was tested in the air (see Fig. 26). 




Figure 26 
Coil of wire in air. 



59 

The number of lines flo-\ving in the coil in Fig. 26 may- 
be ealcnlated by Formula 4, or measured by coil and gal- 
anometer as in Fig. 27. 

Fig. 27 shows the same coil as in Fig. 26, except that 
the coil is fiJled with iron instead of air. 

The number of lines flowing may be measured with a 
small coil and galvanometer. By passing the same currents 
through both coils in Figs. 26 and 27 and comparing the 
number of magnetic lines produced, the permeability of 
the iron is found. 

If there are 100 turns in each coil, and one ampere is 
flowing through each coil, suppose current in coil in Fig. 
26 produces 100 lines and current in coil in Fig. 27 produces 
185,000 lines, then the permeability of the iron is 185,000 
divided by 100 equals 1,850 at this stage of saturation. 




Figure 27 
Same coil as in Figure 26 with iron core. 

In the above table the first column represents the num- 
ber of lines of force which flow through the iron. The sec- 
ond column is the permeability or multiplying power of the 
iron. The third column is the number of magnetic lines 



60 

there would be in air. The fourth column is the ampere 
turns required to force the magnetic lines through one inch 
of iron at the given density. The first part of this table is 
devoted to ordinary wrought iron and may be used in a 
general way to represent the magnetic properties of char- 
coal and sheet iron, soft sheet steel and cast steel. 

The second part of this table represents the properties 
of ordinary cast iron. 

It must be carefully kept in mind that while these ta- 
bles give a general idea of the map-netic properties of iron, 
QO two specimens of iron are exactly alike, and if it is de- 
sired to get an accurate know^ledge of the magnetic quali- 
ties of any particular sample of iron, it is necessary to make 
a separate test for this sample and construct a table similar 
to table Xo. 5 for each sample. It will be noticed that in a 
general w^ay wrought iron conducts the magnetic lines 
about twice as well as cast iron. 

WTien formula (5) is revised, so as to introduce the per- 

a. t. X A X // 

meability of the iron, it becomes N equals (5) 

1 X .3132 

in which /z represents the value of the permeability. 

We will now take an example and calculate the ampere 
turns required to force a given number of magnetic lines 
through the various parts of the magnetic circuit. We will 
select the Edison type of bi-polar dynamo for this calcula- 
tion. The easiest way to' make this calculation is to find 
the number of ampere turns required in each part of the 
magnetic circuit and add together the numbers so found. 



61 



In this example we will find ithe number of ampere 
turns required in the yoke, which is of wrought iron, next 
that required in each magnet core, next that required in 
each pole piece, then that required in each air gap and last 
that required in the armature iron. 

In Fig. 28 the dimensions of the parts have been indi- 
cated and the approximate length of the average magnetic 
line is shown. Let us suppose that 4,500,000 magnetic lines 
flow through the magnetic circuit of this dynamo. This 
will cause 4,500,000 divided by 54, or 83333, to flow per 
sqi'.are inch through the yoke. The following formula may 

Nxlx.3132 
be deduced from formula 4: A. t. equals (6), in 

A X // 




Figure 28 
Magnetic circuit of Edison bipolar dynamo. 



t)2 

which N equals the total flow of magnetic lines in the part 
of the magnetic circuit considered, 1 equals length in inches 
of this part of the magnetic circuit, A equals area in square 
inches of this part of the magnetic circuit; // equals the 
permeability of this part of the magnetic circuit, with the 
particular Talue of N that may exist and the value of u must 
in each casi be found from the table. Substituting these 
quantities in formula (6) we have for the yoke X equals 
4,500,000; 1 equals 22 inches; A, or the area 
of the cross section of the magnetic circuit 
in square inches, which in this case equals 
6 multiplied by 9, or 54; and fi, or the permeability, equals 
1,107. This is found by consulting the table, in w^hich it is 
seen that the permeability of wrought iron equals 
1260 at 80,000 lines per square inch. That the permeability 
at 85,000 lines per square inch is 1030. The permeability 
of 83,333 lines wdll be approximately 2-3 the difference be- 
tween these two permeabilities, or 1260 — 153 or 1107. 

4,500,000x22x.3132 

a. t. equals equals 520 

54x1107 

The a. t. required in the magnet core will be found by 
substituting for N, 4,500,000 as before, for 1 or length of 
this part of the magnetic circuit, 10 inches. 

For A, or the cross section of the magnetic circuit at 
this point, we have 50.26 square inches, which is the area of 
a circle 8 inches in diameter. 

To ascertain the value of fi it is necessary to find out 
how many lines per square inch flow through the magnet 
core. In order to do this, divide 4,500,000 by 50.26, which 
g-ives 89,534 lines per square inch. This is sufficiently close 



63 

to 90,000 lines to take the permeability of 90,000 lines from 
the table, and, substituting* 830 for the value of ^i, we have 

4,500,000xl0x.3132 

a. t. equals equals 338 

50.26x830 

Xext we take up the number of a. t. required in the 
pole piece. This is of east iron and the area of cross sec- 
tion is indicated in the sketch as being 12 inches x 12 inches, 
or 144 square inches. 

The flux per square inch is 4,500,000 divided by 144 
equals 31,?50. The ampere turns required in this part of 
the magnetic circuit would be 

4,500,000x9x.3132 

a. t. equals equals 166 

144x532 

It must be kept in mind that the pole pieces are of cast 
iron and therefore the permeability is much lower than if 
they were of wrought iron. 

The ampere turns required in the air gap are 

4,500,000xlx.3132 

a. t. equals equals 10,313 

138x1 

The air gap in an actual dynamo is partly filled with 
copper wire and insulation, but this conducts magnetic lines 
no better than air. 

The area of the air gap is calculated on the assumption 
that the pole pieces embrace two-thirds of the circuniler- 
ence of the armature. As per the sketch, the pole piece is 
12 inches long and the average diameter of the air gap is 



64 

11 inches, and the circumference of a circle 11 inches in 
diameter is 34.54 inches. One-third of this is 11.5 and the 
area of the air gap is 11.5x12 equals 13S square inches. 

It will be noticed that the numoer of ampere turns re- 
quired in the air gap is vastly greater than that required 
in any other part of the magnetic crrcuit, and is a good 
example of how much better a conductor of magnetic lines 
iron is than air or any ordinary material. The ampere 
turns required in the armature iron are 

4,500,000x9x.3132 

a. t. equals equals 84 

72x2077 

In this part of the circuit the area of cross section 
of the magnetic circuit is taken as 6 multiplied by 12 inches 
equals 72 square inches, because the shaft is 4 inches in 
diameter, and for reasons that will appear later the lines 
cannot flow across the shaft when the armature is in motion. 

There are two coils on the dynamo, one on each magnet 
core,, and each of these two are of equal power and each 
does half the work of driving the magnetic lines around 
the circuit. If we wish to find the number of ampere turns 
that each should supply, we must add together half those 
required for the yoke, all in one magnet core, all in one 
pole piece, all In one air gap, and half those in the armaturS 
iron. Gathering these results together, we have: 

Half a. t. required in yoke ' 260 

All a. t. required in magnet core 338 

All a. t. required in pole piece 166 

All a. t. required in one air gap. .... .10,213 

Half a. t. required in armature iron.. 42 

Total a. t. required in half of mag- 
netic circuit 11,019 



65 



Each of the two coils will then be required to produce 
11,019 ampere turns in order to force 4,500,000 magnetic 
lines around the magnetic circuit. 

The method of calculating the size of wire required in 
the coil to produce this number of ampere turns will be 
explained in one of the succeeding chapters. 

The Edison type of dynamo is an excellent example of 
the older style of dynamos that were built eight or ten 
years ago. The prevailing style for large machines at the 
present time has the multipolar field and ironclad armature. 

The ironclad armature is well adapted for all 'sizes of 
machines, while the multipolar construction is especially 
advantageous in machines of large output, but for machines 
of less than 10 H. P. is not so good as the bipolar construc- 
tion, as will be explained in the chapter on Hysteresis and 
Eddy Currents. 

Figs. 29 and 30 show diagrams of the two styles of ar- 
mature in the same field frame. 




Figure 29 
Smooth core armature. 



66 

The chief reason tha.t ironclad armatures have come 
into use is that by means of this device the magnetic re- 
sistance of the air gap is very much reduced. 

The practical effect of the introduction of the ironclad 
armature is to make the carrying capacity of the iron of 
the magnetic circuit the limit of the flux through the cir- 
cuit. 

The resistance to the magnetic flux in the air gap of 
the ironclad armature is not over one-fifth that in a smooth 
core armature of the same capacity. The ironclad arma- 
ture may be run so that there is only enough room between 
the armature iron and the iron of the field frame to permit 
of mechanical rotation- 
It will be noticed that the wire on the ironclad arma- 
ture is buried in slots, cut in the armature. This protects 
them from mechanical injury, and, more important still. 




FignreSO 
Iron clad armature. 



67 



gives them perfect mechanical support, so that there is no 
tendency to slide or move from their places as there is in 
the smooth core armature. 

'Practically all of the magnetic flux that passes into the 
armature must get through the bottom of the iron teeth of 
the armature, and the area of this part of the magnetic cir- 
cuit determines the total flux that can be used. 

We w^ill now calculate the ampere turns required in a 
bi-polar machine v^ith an ironclad armature, and also the 
ampere turns required in a six-pole field with ironclad ar- 
mature. 




Figure 31 

Magnetic circuit of 5 H. P. bipolar machine with iron clad armature, 

and cast iron field frame. 



68 



The bipolar machine is shown in Fig*. 31 and the dimen- 
sions are those actually used in a 5 H. P. motor. 

It will be noticed that in this machine the yoke is in 
two parts and half of the flux flows through each part. 



The frame is so designed that the fliix is most dense 
in the frame in the pole pieces. The sectional area 
of the pole pieces is show^n in Fig. 32. 
The area will be 9x51/, or 49f/C, less what 
is cut off of the corners. A circle 3 inches 
in diameter has an area of about 7 square 
inches, which is 2 square inches less than a 
surface 3 inches square, so that the area of 
the pole piece will be 491/2 minus 2 equals 
4714 square inches. 

This machine has a flux of 2,100,000 
lines. At this flux the density in the pole 
piece will be 2,100,000 divided by 47^^ equals 
44,210. 



Oi 



SI 



Figure 32 



Calculation of 

Sectional 

area of pole piece. 



The average length of the magnetic line 
in each pole piece is 4 inches. 

The permeability of cast iron at 44,1^0 is 153. Substi- 
tuting in the formula Ko. (6) we have 

2,100,000x4x.3132 

a. t. equals equals 362 in each m.agnet core. 

47.5x153 



The flnx in the yoke can all be calculated at the same time, 
for the density all through the yoke is the same, and 
consequently the value of the permeability or /i is the same. 



aux is 2,100,000 divided by (2%xl0x2) equals 2,100,000 divid- 
ed by 52.5 equals 40,000. The permeability at 40,000 lines 
per square inch in cast iron is 245. Substituting we have 



2,100,000xl2x.3132 



a. t. equals 



equals 613 



52.5x245 
in each half of the yoke. 

The area of the air gap is not the whole area of the pole 
face, for with an air gap 1-16 inch long there is a bunch- 
ing of the lines to a greater or less extent, as shown in 
Fig. 33. 

It is important to calculate the area 
of the air gap carefully, for on this will 
depend the number of a. t. in the air 
gap, and this number is much greater 
than that for any other part of the 
circuit, and an error in this calculation 
will have a greater effect on the total 
result than in any other. 

There are 48 sloits in a disc 7l^ 
inches in diameter and each slot is .230 
inches wide; the circumference of the 
disc is 23.55. Each slot and tooth 
take up 23.55 divided, by 48 equals .491. 
This leaves the top of the tooth .491— 

.230 equals .261 wide. The lines will spread from the top of 
the teeth to the iron pole piece. Each pole piece embraces 
or covers 16 teeth. Experience teaches 'that it is safe to 
assume that the lines spread from the top of the teeth, so 
that the top of the tuft is equal in width to the ^op of the 
tooth plus twice the width of the air gap, but the average 




Figure 33 

Bunching of magnetic 
lines in air gap. 



70 

width will be only half this. The average width of the tuft 
will be .261 plus .062 equals .323. 

Since the length of the armature is 51/2 and there are 
48 teeth in the armature, we have 16 tufts of lines each 5^^ 
inches long x .323 wide. The area of the air gap is then 
16x5.5x.323 equals 28.4. Substituting w^e have 

2,100,000xlx.3132 
a. t. equals equals 1447 

28.4x16 

The magnetic lines are very much crow^ded in the arma- 
ture teeth, and the density changes at each point in the 
length of the teeth, so that theoretically a separate calcu- 
lation w^ould have to be made for each part in the length of 
the tooth. A sufficiently close approximation, however, may 
l)e made by making two calculations, one for the ampere 
turns required for a length of i/g inch at the bottom of the 
teeth and the other for the rest of the tooth. 

It is first necessary to find the area of the "bottom of the 
teeth. 

The slots are % inch deep, .230 inches wide a.nd round 
at the bottom. This being so, the narrowest place in the 
tooth will be .750 minus .115 equals .635 from the outside of 
the disc, for there is a circle .230 in diameter at the bottom 
of the slot. 

The circumference of a circle whose periphery passes 
through the narrowest part of the tooth is 

3.i416x[7.5— .0:55x2] equals 3.1416x6.23 equals 19.57. 

1-48 of this circumference equals .408. 

.408 — .230 equals .178 inches, which is the width of the 
tooth at its thinnest point. 



71 

The area of the tooth at the bottom is .178x5.5x16 equals 
15.66. 

The flux at the bottom of the teeth is 2,100,000 divided 
by 15.66 equals 134,100. 

The permeability at this flux is 30 — 4-5(30 — ^24) equals 
25. Substituting 

2,100,000xlx.3132 

a. t. equals equals 210 

15.66x8x25 

As indicated above, the ampere turns in the rest of the 
tooth may be found in one calculation. The width of the 
teeth !n the narrowest place is .178 and in the widest place 

.2614-.178 

is .261. The average width is then equals .219. 

2 
The average area of the teeth will be 

.219x5. 5x'l'6 equals 19.3 square inches. 
This area gives a flux of 2,100,000 divided by 19.3 equals 
109,000, and the permeability at this density is 280 — 4-5 
(280 — 175) equals 19G. Substituting we have 

2,100,000x5x.3132 

a. t. equals equals 108 

19.3x8x196 
The last calculation to make is ampere turns required 
for the armature iron. 

The area of iron carrying lines is 5V3x[7i^ — (IVs-j-lVi)] 
equals 4%x5i/< equals 26.1. 

The flux per square incTf ^vTif he 2,100,000 divided by 
26.1 equals 80,460. 

The permeability at this density equals 1,237. 
The a. t. required for armature iron 

2,100,000x5x.3132 

a. t. equals equals 102 

26.1x1237 



72 

Collecting" our results we have: 

A. t. required in eaeli mag-net c<ore 36S 

A. t. required in each half of yoke 613 

A. t. required in each air g*ap 1,447 

A. t. required in bottom of teeth on one side. . 210 

A. t. required in body of teeth on one side ' 108 

A. t. required in half armature iron 51 

A. t. required in half magnetic circuit 2,791 

We must then have two coils each with a magnetizing* 
power of 2,791 ampere turns, or one coil with a magnetizing* 
power of twice this, in orijer to force 2,100,000 lines around 
the circuit. It wall be noticed that the number of ampere 
turns required in the air gap is over one-half the total am- 
pere turns required. A little thought will show also that a 
small decrease in the flux would decrease the mag'netizing* 
pow^r very greatly, and, if it w^as necessary to force a little 
more flux through the circuit, a great deal more magnet- 
izing power would be required. This is because the iron 
in the motor just calculated is almost saturated, and in 
some parts of the circuit is saturated. A small decrease in 
the flux would very greatly imcrease the permeability and 
so decrease the magnetizing power required in these parts ol 
the iron magnetic circuit. 

It will be seen that it is not possible to obtain exact, 
results in making these calculations, for the permeability 
of the actual iron may be more or less than that given in 
the table. 

It will usually be found that the table is a little high 
for wrought iron and cast steel and about right for good 
soft sheet steel. The writer has used samples of cast iron 



73 

that were better than those given in the table, and also 
some that were worse. It is easy to get cast iron as good 
as that shown in ithe table. 

An equally close approximation to the ampere turns 
required in the iron part of a machine may be had by taking 
the ampere turns required for one inch of iron at a density 
given by the table. 

Use the density closest to the one required, and if any 
mistake is made, make the result too large rather than too 
small. 

The ampere turns required in the magneti<i circuit of 
the six-pole machine shovm in Fig. 34 has been obtained in 
this way. 




Figure 34 
Magnetic circuit of a 100 K. W. Westinghouse dynamo. 
6 



J. 



74 

These figures are taken from a TVestinghouse 100 K. W. 
dynamo. 

In this machine we will make six calculations, for the 
pole pieces are made of thin pieces of sheet iron riveted 
together. This makes the pole piece wrought iron and the 
yoke cast iron, and thus requires two calculations for this 
part of the magnetic circuit. In these calculations the fol- 
lowing notation will be used: 

equals number lines per square inch. 

1 equals average length of magnetic circuit in the part 
of machine under consideration. 

A equals cross sectional area. 

// equals permeability. 

a. t. equals ampere turns. 

For the laminated pole piece 

2,500,000 

O equals equals 55,000 

61/2x7 

1 equals 7. 

A equals 45}^ square inches. 

// equals 2331. 

From table ^o. 6 it is found that it will take ' .53 a. t. 
at this value of fi to force the lines through one inch of the 
iron; therefore it will take 7x7.53 equals 53 a. t. to force the 
lines through the whole of 1. 

For the yoke which is of cast iron 

A equals 40 square inches. 

1 equals lO^/j inches. 



75 



2,500,000 

O equals equals 31,250 

2x40 

a. t. per inch equals 14 6. 

Total a. t. equals 10.5x14.6 equals 153. 

For the air ^ap: 
1 equals % iuch. 
Width of top of tooth 

20x3.1416 

—.359 equals .539 

70 

Number of teeth under each pole 7.4. 

Average wid*th of air space between one tooth and pole 
face equals .539-J-.125 equals .664. 

A equals .664x7.4x7 equals 34.4. 

2,500,000 

O equals equals 72680 

34.4 

More accurate results will be obtained by using formula 
(6) in calculating" the a. t. in the air g-ap, for in this part of 
the magnetic circuit there is no value of fi to be inserted. 
Substituting" in formula (6) the a. t. required for tl'e air 
gpap is found to be 

2,500,000xlx.3132 

a. t. equals equals 2845 

34.4x8 



76 

A. t. required in Yq inch at bottom of tooth. 

1 equals y^ inch. 

Diameter of circle through the thinnest part of tooth 
equals 20 — 5-|-.359 equals 15.359 inches. 

Width of tooth here 

3.1416x15.359 



-.359 equals .330. 



70 
A equals .330x7.4x7 equals 17.1. 

2,500,000 

O equals equals 146,200. 

17.1 

146,200 lines per square inch is beyond the Mmits of the 
table, but it will require about one-fifth more ampere turns 
per inch over 2,434 as the difference between the a. t. re- 
quired at 135,000 and 140,000, or 2434+[6-5 (2434— 1761)] 
equals 3242. Hence 

A. t. equal® 1/8x3242 equals 405. 

A. t. required in remainder of tooth: 

L equals 2.5 — Vg equals 2%. 

(.3304-.539) 
A equals x (7.4x7) equals 2-2.5 square inches. 



2,500,000 

O equals equals 111.110. 

22.5 



77 



A. t. equals 23/8x237 equals 563. 

A. t. required in rest of armature iron: 

If the shaft and spider are 10 inches in dianneter, the 
area of armature iron carrying* lines equals 20 — (5-r-10)x7 
equals 5x7. 

A equals 5x7 equals 35. 

L equa'ls 3% in one-half of armature. 

2,500,000 

O equals equals 71,500. 

35 

A. t. equals 3yoXl3.6 equals 47. 

Summarizing our results we have: 

A. t. in one pole piece 53 

A. t. in yoke 153 

A. t. in air g-ap 2,845 

A. t. in bottom of teeth 405 

A. t. in body of teeth. 563 

A. t. in armature iron 47 

Total 4,066 

The coil on each pole piece wull have to be capable of 
producing 4,066 ampere turns in order to force 2,500,000 
lines through each one of the six magnetic cii^cuits. 






QUESTIOlSrS ON CHAPTER IV. 



1. On wha4 does the strength of a helix carrying a cui^ 
rent depend? 

2. Is there any relation between the number of mag^ 
netic lines generated by a current in a helix, the miagnetiz- 
ing power of the helix and the magnetic reluctance offered 
by the path which the lines take? If so, what? 

3. If the equation of a magnetic circuit be compared 
to Ohm's law what quantity in the magnetic circuit corre- 
sponds to the current? What corresponds to the voltage? 

4. To what is the magnetic resistance of a circuit pro- 
portional? 

5. What is the effect of the introduction of iron into 
a helix? 

6. ^Xiiy is it that a number of magnetic lines traversing 
a circuit is increased more by placing a piece of iron inside 
the helix than by tilling the space around the outside of the 
helix with iron? 

7. How many magnetic lines will flow through a helix 
three inches in diameter and five and one-half inches long 
upon the supposition that the magnetic lines meet with no 
resistance except that encountered passing through the in- 
side of the helix; the helix has ninety-five turns and fifteen 
amperes? 

8. If the number of amperes in the helix in No. 7 be 
increased to twenty-one how many magnetic lines will flow? 



79 

9. What is permeabilityt 

10. Why is it true that Formula No. 4 is not true when 
iron is used in the in«agnetic circuit? 

11. When is the permeability of iron low? 

12. When iron contains a great many magiietic lines 
what is said of its magnetic condition? 

13. Why is it that the magnetic circuit of a dynamo is 
almost entirely composed of iron? 

14. How is the permeability table obtained? 

15. What may be said in a general way of the permea- 
bility of wrought iron, common sheet iron, boiler plate and 
cast steel? 

16. Is table Xo. 4 an exact representation of the per- 
meability of any particular sample of wrought iron or 
steel? 

17. In a general way what are the permeabilities of 
cast and wrought iron? 

If., In calculating the number of ampere turns requir- 
ed for a magnetic circuit why is it usual to calculate the 
number in each part of the circuit and add them together? 

19. How many ampere turns will be required to force 
1,300,000 lines around the magnetic circuit shown in Fig. 
35? 

20. Give ampere turns required in half of yoke, in pole- 
piece, air gap, body of armature teeth, neck of armature 
teeth and in armature. 

21. How many ampere turns will be required in each 
field coil in Fig. 34, provided 2,300,000 lines of force flow? 
Give ampere turns in each part of the magnetic circuit as in 
preceding question. , 



dO 



22. Why is it necessary to be more careful in calculat- 
ing the dimensions of the air gap than with other parts of 
the magnetic circuit? 

23. If a field core is made of cast steel, what will be its 
sectional area as compared with a core made of cast iron 
capable of carrj'ing the same number of lines? 

24. How many ampere turns will be required to force 
1,000,000 lines around a ring averaging one foot in diameter, 
having a sectional area three and one-half inches in diame- 
ter? 




Figure 35 



81 

25. What, besides iron, are the magnetic metals? 

26. Are the copper and insulation used on an armatur^e 
more permeable than the air which they displace? 

27. What is a smooth core armature? 

28. What are the advantages of iron clad armatures? 

29. What is the effect of using a toothed armature on 
the distribution of lines of force passing from the pole 
piece? 

30. What is the area of the air gap in a dynamo having 
thirty-six teeth in the armature, one-third of the arm-ature 
teeth under each pole; the armatoire teeth .310 inches wide 
at the top, the air gap one-sixteenth of an inch wide and 
five inches long? 

31. How many ampere turns will be required in the 
air gap to produce a flux of 5,000 lines crossing the air gap 
between the poles of a horseshoe magnet and its arjnature 
w^here the area of the face of the magnet is one-half of one 
square inch and the air gap is one-fourth of an inch long? 

32. What is the usual flux employed in the bottom of 
armature teeth? 

33. What will be the effect of reducing the ampere 
turns ten per cent, in the motor show^n in Fig. 29? 

34. Why is it that the number of magnetic lines which 
flow through an air gap is proportional to the ampere turns 
acting on the air gap, while the number of magnetic lines 
flowing through the rest of the magnetic circuit is not pro- 
portional to the ampere turns? 

35. Why is it impossible to obtain absolutely correct 
results in calculating the ampere turns required for the 
ampere turns of a magnetic circuit? 



CHAPTER V. 



MAGNETIC TRACTION. 



It is a well-known fact that the north and south poles 
of two magnets attract each other. In fact, the magnetic 
lines act as if they were elastic cords tiat always tend to 
shorten themselves. \"\Tien a great number of the magnetic 
lines flow across a given space the attraction is very strong. 

Ewing, in some of his experiments, pushed the mag- 
netism of a piece of soft iron to such a point that the pres- 
sure due to the magnetic attraction was 1,000 pounds per 
square inch. 

Table No. VIT gives the pull between a magnet and its 
armature when the given fluxes pass. The formula from 
which this table was calculated is 

B2 A 
Pull in pounds equals (7) 

72,134,000 

in which B equals the flux in lines per square inch, A equals 
the area of cross section between magnet and armature in 
square inches. 



83 

TABLE No. Vn. 



Flux per sq. in. between Pull in lbs. per sq. in between 

armature and magnet. armature and magnet. 

5,000 .34 

10,000 ^ 1.4 

15,000 ' 3.1 

20,000 5.5 

25,000 8.7 

30,000 12.5 

35,000 20.0 

40,000 22.2 

45,000 28.1 

50,000 34.6 

55,000 41.9 

60,000 49.9 

65.000 58.5 

70,000 67.9 

75,000 78.0 

80,000 88.7 

85,000 100. 

90,000 112. 

95,000 125. 

100,000 138. 

105,000 153. 

110,000 168. 

115,000 183. 

120,000 199. 

125,000 216. 

130,000 234. 

135,000 252. 

140,000 272. 



84 




Figure 36 

Best forms of magnet for 
lifting purposes. 



The best form of magnet for traction or lifting pur- 
poses is shown in Fig. 36. 

Fig. 30 shows n cross sec- 
tion of a magnet and its ar- 
mature. In this case it is de- 
sired to force as ^many lines 
of force as possible across the 
joint between the armature 
and magnet and also to re- 
duce this area as much as 
possible, for it must be kept in mind that if we can get the 
same iiux across a joint -that has an area of 6 square inches 
as flows across another joint having an area of 12 square 
inches, the pull in pounds in the first case will be twice 
what it would be in the second case. This is because the 
pull is proportional to the square of the number of lines 
per square inch flowing. 

A magnet shaped as in Fig. 36 is easily and cheaply 
made and by its shape protects the winding inside it. 

The writer designed a set of magnets for fastening a 
drilling machine to the bottom or sides of an iron vessel. 
These magnets, which would lift from 1,000 to 1,200 pounds 
each, weighed 11 pounds each. 

A flux of 140,000 lines is as high as it is possible to go 
with ordinary steel, and higher than some steels will carry. 
Assuming that we have steel that will carry 140,000 lines, 
we would have a pressure of 272 pounds per square inch. 
Allowing 100,000 lines per square in. in the rest of the mag- 
netic circuit and 140,000 at the joint between the armature 
and field, what will be the lifting power of a magnet 9 
inches in diameter? 



85 




First, assume the magnetizing- coil to be one inch wide 
bj^ two inciies deep. (Fig. 37). 
The sizes must be so selected 
that the area of the outside of 
the magnet equals that inside 
the magnet, for as many lines 
pass into the armature outside 
the coil as pass out of it inside Figure 37 

the coil. Pull of iron clad magnet. 

The sizes indicated do this very nearly; the area of 
each part is equal to the area of a circle 5^/4 inches in diam- 
eter. Table No. 13 gives this as 21.65 square inches. At 
100,000 lines per square inch there would be 2,165,000 lines 
in the magnet. 

If the surface is cut away, as indicated, so as to compel 
the lines to pass into the armature at a density of 140,000 
lines per square inch, the area of contact will be 

ei.65xl0 

equals 15.5 sq. in. 

14 



As the pull across this surface is 272 pounds per square 
Inch, the total pull on both poles of the magnet will be 
15.5x272x2 equals 8,432 pounds. 

The thickness of the armature should be such that the 
lines as they flow from the outside toward the center, as 
shown in the sketch, should never be crowded to more than 
100,000 lines per square inch. In the magnet shown in Fig. 
37, the point in the armature at which the lines wdll be 
most crowded will be a circle 5i^ inches in diameter directly 
under the south pole of the magnet. 



86 

The surface across which the lines pass is an area equal 
to the circumference of a circle 5l^ inches in diameter or 
16.5 inches x the thickness of the armature. Since the area 
will have to be 21.65 square inches the thickness will be 
21.65 divided by 16.5, or very nearly 1 5-16 inches 

A magnet of this shape is used in some of the electric 
brakes used on some of the suburban cars.- 

Here the armature cons-titutes part of the wheel on 
-which the car runs, and the magnet is stationary. 

When current is thrown into the magnet it attracts the 
armature or wheel, thus tending to lock the wheel. 

There is enough residual magnetism dn the iron to hold 
the car at a standstill on an ordinary grade without the 
use of hand brakes. 

Magnets are coming into general use for many pur- 
poses. They are used in some rolling mills for handling 
heavy steel ingots and for loading boiler plate on to cars, 
and will doubtless find a greater use as their capabilities 
become better known. 



QUESTIO]N^S ON CHAPTER V. 



1. What is magnetic traction? 

2. How great a pressure per square inch has 'been pro^ 
duced by magnetic traction? 

3. Suppose only a small number of ampere turns can 
be secured to attract an armature, why is it that enlarging 
the pole pieces and armature and therefore the air gap in- 
creases the pull? 

4. Why is it that the area of contact between the arm- 
ature and magnet in Fig. 33a was reduced in order to in- 
crease the magnetic traction? 

5. A certain wheel on an inter-urban street car carries 
a weight of five tons; a pressure of one and one-half tons 
is required on the brake shoe in order to make this wheel 
slide on the rail; design as light a magnet as possible, one 
foot or less in diameter, that will give the pressure between 
magnet and car wheel when car wheel is used as the arma- 
ture to make the wheel slip on the track. 

6. A solenoid of the shape shown in Fig. 38 has an 
armature shaped like a horseshoe; how many amperes will 
have to flow through the solenoid in order to lift 100 pounds 
provided the iron core of the solenoid is two inches in diam- 
eter and there is a space of one inch between the stationary 
and movable iron parts of the magnetic circuit? 

7. What is the best shape for a magnet for lifting puiv 
poses? 






88 



8. How many ampere turns will be required to produce 
a lifting power of 2,5D0 pounds in an iron c^d magnet six 
inches in diameter, provided the slot for the coil is three- 
fourth inches wide and the surface between the armature 
and the magnet is 80 per cent, of the sectional area of the 
magnet? 




Figure 38 



CHAPTER VL 



MxVGNETIC LEAKAGE. 



In dealing with the calculation of the magnetic circuit 
it niust be clearly kept in mind that all the magnetic lines 
do not pass through the magnetic circuit as calculated. 
The air will carry lines of force and does carry a great 
many. The magnetic lines that are generated by the field 
coils and that do not pass around the magnetic circuit and 
through the armature are called leakage lines. 

In the two figures (39 and 40) are shown the paths of 
the leakage Hues in two styles of dynamo. 



\" 



"^"^mm^ 




Figure 39 
Magnetic leakage in "bipolar dynamo, horseshoe type. 



J. 



90 



In the Edison machines as actually made the leakage 
coefficient is 1.4. That is, out of 140 lines produced in the 
field cores only 100 pass throug-h the armature. 

In the other style of bipolar machine the leakage co- 
efficient is less than 1.1. The reason that it is so much 
lower is that only a small surface of fully charged pole is 
exposed to the air. 

In the ca'se of the Edison dynamo ,Fig. 39) the very 
large pole pieces N. and S. are exposed to the air and al- 
most the full number of ampere turns tend to drive lines 
from !N. to S. through the air gap and armature and also 
through the air. In Fig. 40 not 1-10 the surface in propor- 
tion is exposed for leakage. 




Figure 40 
Magnetic leakage in internal pole bipolar frame. 

Another great advantage of the internal pole type is 
that what leakage there is is inside the machine, where it 
is not apt to draw wire nails and bits of iron dust; but in 
the case of the Edison dynamo the magnetic leakage will 
attract all the iron that comes in its neighborhood, and 
there is danger of pieces of iron being drawn into the arma- 
ture. 



91 



TABLE NiO. Vin. 



Diagrams of magnetic circuits of several dynamos and their 
leakage coefficients. 




Diagram of magnetic circuit of Sdison dynamo. 
Leakage coefficient 1.4. 




Diagram of magnetic circuit of T. H, bipolar dynamo. 
Leakage coefficient 1.3. 



(JJ^iKi^ 



»|jinjjii^ 



Diagram of magnetic circuit of Westlnghouse 4-pole dynamo. 
Leakage coefficient 1.1, 



r. 



92 




Diagram of magnetic circuit of Lincoln 2-pole dynamo. 
Leakage coefficient 1.1. 




Diagram of magnetic circuit of G, E. 14-pole alternator dynamo. 
Leakage coefficient 1.25. 




Diagram of magnetic circuit of Siemans & Halske dynamo, 
4-pole field inside armature. Leakage coefficient 1.08. 




Diagram of magnetic circuit of Manchester type 
Leakage coefficient 1.5. 



QUESTION'S OX CHAPTER VI. 

1. What is magnetic leakage? 

2. What is the relative conductivity of air and iron aa 
used in a dynamo for magne-tic lines? 

3. How is it possible to design a machine so that the 
magnetic leakage will be reduced to a minimum? 

4. Why is it that an Edison dynamo has so many more 
leakage lines than an internal pole machine such as shown 
in Fig. 36? 

5. In Fig. 25 it was assumed that all the lines flowed 
through the iron teeth into the armature. How many lines 
will leak through the slots occupied by the wire? 

6. How many lines will leak across the space in which 
the armature revolves if the armature is removed in Fig. 29? 

7. Why is it that there is such a great amount of mag- 
netic leakage and so small an amount of electric leakage in 
ordinary circuits? 

8. Does the fact that a djmamo has great magnetic 
leakage impair its efficiency greatly? If so, why? 

9. Xame ather disadvantages of magnetic leakages. 

10. What are the advantages of the internal pole type 
of machines as compared with the horseshoe magnet type? 

11. What is a coefficient of leakage? 



/ CHAPTER Vn. ' 

ENERGY IN ELECTRIC CIRCUITS. 

It is a well-known fact that when current flows through 
an electric circuit in sufficient quantity heat is developed. 
The incandescent lamp is the most ordinary example of this. 
Experience will prove that doubling the amount of current 
through a resistance without changing the voltage doubles 
the heat produced in The resistance. Also doubling the 
Toltage tending to drive 'current through resistance without 
changing the current doubles the heat produced. This 
may be very easily proved by making the experiments indi- 
cated in Figs. 41, 42 and 4o. 




VOLTS ' 



Figure 41 
Certain heat produced in lamp 




II0VCLT5 
I AMR 



Figure 42 
Twice as much heat with san ^ 
voltage and twice the current 




Figure 43 

Twice as much heat as Figure 37 with double voltage 

and same current. 



k^ 



95 

It is clear that the energy in the electric circuit is pro- 
poHional to the current and also to the voltage or to the 
product of voltage and current. 

Energy in'an electric current is measured in watts, and 
we may write watts equals amperes x volts, or 

W equals CxE (S) 
Substituting in (8) its value from Ohm's law C equals 

E 

R 
— (See Chap. I.) 

We hav^ 

E E2 

W equals — xE equals — (9). 
R R 

Again substituting in (8) the value of E from Onm*s 
law equals CxR. 

W equals CxCxR equals C2R (10). 

Putting (8), (9) and (10) in words: 

Watts equals amperes x volts (8). 
Watts equals (volts x volts) divided by ohms (9). 
Watts equals amperes x amperes x ohms (10). 
746 watts equals one horse power. 

These formulae should be carefully studied and thor- 
oughly committed to memory. Suppose it is required to 
find how many horse power a certain motor is using from 
the circuit supplying the power. First measure the voltage 
at which current is delivered, next measure the current. 

Suppose a circuit supplying power has 240 " volts 



96 

and "that a motor is taking 15 amperes. From formuls 
(8) we have watts equals 240x15 equals 3600 watts. Th€ 
horse power equals the fwatts divided Tdj 746, or H. P. equals 
3600 divided by 746 equals 4.83. 

Suppose the same current was used in a (heater or a 
wire resistance, the resistance would be 

E 240 

R equals — equals equals 16, 

C 15 

If now formulae (8), (9) and (10) are correct, all three 
should give the same result in watts. We have 

Amperes equal . . I 15 

Volts equal 24u 

Ohms equal 16 

Watts equal , 3600 

Formula (8) is watts equals amperes x volts equals 
15x240 equals 3600. 

Formula (9) is watts equals volts x volts divided by 

240x240 

ohms equals equals 3600. 

16 

Formula (10) is watts equals amperes x amperes x 
ohms equals 15x15x16 equals 3600. 

If the shunt field coil of a dynamo takes 2^2 amperes at 
200 volts, what is its resistance and how many watts is it 
using? 

E 200 

Ohms equals — (3) equals equals 80. 

C 2.50 

Watts equals ExC equals 200x2% equals 500 or about 2-3 
H. P. • 



97 

If a series dynamo has 10 amperes flowing' through its 
field and the resistance of the wire is 3.6 ohms, how many 
watts is it using- and how many volts are required for this 
part of the circuit? 

Volts equals CxK (2) equals 10x3.6 equals 36. 

Watts equals C^R equals 10x10x3.6 equals 360, or a little 
less than y. H. P. 

Suppose the current in a long distance power transmis- 
sion plant is 300 amperes and that the voltage at the receiv- 
ing end is 750 volts less than at the sending end, what is the 
resistance of the line and how many H. P. are lost due to 
the resistance? 

E 750 

E equals — (3) equals equals 21/2 ohms. 

C 300 

Watts equals CxE (12) equals 300x750 equals 225,000. 
H. P. equals 225,000 divided by 746 equals 301.6 H. P. 

If the voltage at the sending end was 10,000, what was 
the proportion of power delivered to that received? 

Power delivered to line, watts equals 300x10,000. 

Power received from line, watts equals 300x9,250. 

925 

Ratio equals equals 92.5%, or efficiency of trans- 

1000 
mission line. 

Why is it that high voltage is used in all the long dis- 
tance power transmission plants? A study of formulae 
(8), (9) and (10) will answer this question. 



98 

Suppose H is desired to transmit 50 H. P. five miles. 
The watts will be 50x746 equals 37,300. If this is generated 
at 250 volts the current will be 37,300 divided by 250 equals 
149 amperes. 

If the line has a resistance of ^2 ohm, the vo]ts lost in 
the line will be 149x1/2 equals 74.5. The efficiency of trans- 
mission wijl be 

(250— 74.5)x300 175.5 

equals or about 70 per cent. 

250x300 250 

That is, 30 per cent, of the power is lost in the line. 

If now the same power be generated at 500 volts, the 
amperes will be 37,300 divided by 500 equals 74.5 amperes. 
The volts lost on the line will be 1/3x74.5 equals 37.25. The 
efficiency of transmission 

(500— 37.25)x74.5 

equals 92.50 

500x74.5 

In this case only 7V^% of the power was lost. If we 
should repeat the calculation at 1000 volts we would see 
that only % of 71/2% would be lost, or less than 2%. That 
is, 50 H. P. transmitted at 250 volts loses 30%, and at 1000 
volts less than 2%. 

The power lost in transmission is inversely proportional 
to the square of the voltage with a given line. 

The use of high voltage enables a small and cheap line 
to transmit the same power with the same loss that a line 
with lour limes as much copper in it would transmit with 



99 

the same loss at half the voltage. A little thought will show 
that the line loss is proportional to the square of the dis- 
tance from the generating station if equal amounts of cop- 
per are used in all the lines. Thus a line one mile long 
having 1000 pounds of copper will have a resistance of .85 
ohms; a line two miles long having the same 1000 pounds 
of copper in it will have a resistance of 3.4 ohms, or four 
times as much. If the same current is sent over both lines 
there will be fo'jr times as much loss in the two-mile line 
as in the one-mile line. But if. at the same time that the 
length of the line is doubled the voltage is also doubled, 
100 H. P. can be transmitted over the long line with the 
same loss as over the short one. Thus, with a given line 
loss and a given amount of copper in the line, the distance 
to which power can be transmitted is directly proportional 
to the voltage. 

In calculating watts lost in an armature, it is necessary 
usually to find the current flowing through it and find the 
resistance of the armature and use these two factors to find 
the watts lost. 



QUESTIONS ON CHAPTER VII 



1. Wha.t are the three formulae represep^^'diiC power in 
an electric circuit? 

2. How many watts are there in one horse power? 

3. How many watts are expended in a circuit feeding 
a number of heaters if the currrent is eight amperes and 
bhe E. M. F. 500 volts?- 

4. How many amperes are flowing- in a circuit which 
consumes five and one-half horse power at 110 volts; at 
1,000 volts? 

5. What is the resistance of a feed wire in which eight 
H. P. are lost when 300 amperes are being carried by the 
line? 

6. What H. P. is developed by a dynamo which deliver?. 
400 amperes at 250 volts? 

7. What is the per cent, drop in a feed wire in which 
■fiv^e H. P. are lost when 250 amperes are flowing, and the 
dynamo producing the current thas an E. M. F. of 300 volts ?| 

8. Is it possible to determine the resistance of the arm- 
ature in question 6 from the data given in tha-t question? 
If so w^hat is the resistance? 

9. How much current is used on a lamp that require! 
64 watts on a 110 volt circuit? 

10. How maiiy amperes equal one H. P. on a 110 voll 
circuit? On a 220 Volt circuit? On a 500 volt circuit? 0] 
a 1,000 volt circuit? On a 10,000 volt circuit? 



101 

11. How many amperes are there in a kilowatt or in 
1,000 watts or in a K. W. in circuits of each of the voltag^es 
specified in qnestioo. 10? 

12. Why is it that the Edison three-wire system is 
economical of copper? 

13. Would a five-wire system on the lame plan be more 
or less economical? Why? 

14. Why is high voltage used for distriboiting power to 
great distances? 

15. Would it be practicable to transmit 100 H. 
P. over a line having three and one-half tons of copper in 
it to a point five miles away if 250 volts w^ere used? 

16. Would it be practicable with 500 volts; with 1,000 
volts; with 20,000 volts? 

17. Why is it that that with the same cost for copper 
the power loss increases as the square of the distance from 

the power station? 

• 

IS. In what ratio does the loss of power decrease with 
increasing voltage, cost for copper remaining the same? 

19. What is the ratio of distance to which power may 
be transmitted and voltage of supply with constant cost for 
copper and constant line loss? 

20. What will be the cost for copper at .15 per pound 
for a line that will transmit power for 500 — 55 watt lamps 
at 250 volts on a three-wire system perfectly balanced ^^ 
mile from dynamo if current is supplied to lamps at 110 
volts? 



102 

21. Suppose a dynamo is supplying a power circuit at 
125 volts and it is desired to light 300 — 55 watt lamps at a 
pressure of 110 volts 2,500 feet away. Two methods can be 
used for lighting these lamps; a large wire can be run from 
the dynamo to the lamps, in which there will be a drop of 
15 volts. A second method is to drive a 650-volt dynamo 
from the same engine that drives the 125-volt dynamo, op- 
erate a motor on the 650-V'olt current and drive a second 
dynamo working at 110 volts to light the lamps. If copper 
costs .15 per pound, and three extra electric machines cost 
$1,500, which will be the cheaper installation? 

22. If one horse power is lost in 1,000 feet of No. 0000 
wire with a drop of 35 volts, what current is the feeder car- 
rying? 

23. Why is it that in calculating the number of watts 
lost in an armature that formula No. 14 is usually employed? 



CHAPTER Vni. 

CALCULATION OF MAGNET COILS. 

• 
As shown in the chapter on the magnetic circuit it is 
possible to find how many ampere turns are required to 
force a given magnetic flux over a given magnetic circuit. 
After it is discovered in this way how many ampere turns 
each coil should produce, it is necessary to select the size of 
wire and determine 'the amount that should be used to pro- 
duce the desired result. 

The magnetizing power of any coil is measured in 
ampere turns, or the product of the amperes which flows 
through the wire, multiplied by the number of times it cir- 
culates around the core. The meaning of the term is al- 
most self-evident. 

A very peculiar fact becomes apparent upon examining 
the number of ampere turns produced b}" a given coil when 
exposed to the same voltage. Take, for instance, a coil 
wound around an iron core 3% inches in diameter; let the 
thickness of the magnetizing coil be such that the average 
diameter of the coil will be 3% inches, so that the average 
length will be one foot. If this coii is wound with one 
pound of No. 16 wire it will have, as shown by Table 1, 124 
turns. 

The resistance of such a coil will be .515 of an ohm. 
If such a coU is exposed to a pressure of 50 volts, 97.1 
amperes will flow through it, and the ampere turns pro- 
duced by the coil will be 97.1x124, or 12,040. 



104 

If twice as much wire be used on this coil, the ampere 
turns will not be twice as great as might be expected, but 
will remain the same. TLe only dirt'erence will be that 
instead of 97.1 amperes flowing through the coil, only half 
of this, or 48.55 amperes will flow. 

It will be seen that doubling the amount of wire on a 
coil has doubled the number of turns, but also doubled 
the resistance of the coil so as to reduce the current to one- 
half. 

The product of donble the number of turns multiplied 
by half the number of amperes which we have in the sec- 
ond coil produces the same number of ampere turns as 
were produced by the first coil. Increasing the weight of 
the coil then simply decrease the amount of current re- 
quired to produce a given number of ampere turns. 

To produce a greater number of ampere turns in this 
same coil, it will be necessary to wind the coil with larger 
wire, or to increase the voltage applied to the terminals of 
the coil. By using a wire of twice the sectional area of 
No. 16, double the number of ampere turns will be pro- 
duced, or if the average length of the coil instead of being 
one foot is two feet, a wire of double the sectional area of 
No. 16 will be required to x^roduce 12,040 ampere turns at 
50 volts. If at the same time that the average length of 
the turn was increased from one foot to two feet, the volt- 
age was raised from 50 volts to 100 volts, No. 16 vnre would 
still continue to produce 12,040 ampere turns. 

Putting these considerations into the form of an equa^ 
tion we have: 

llVo X A T X L 

A equals 

E 



105 



in which A is area of the ^are in circular mils or is the 
square of the diameter in thousandths of an inch. 

A. T. equals ampere turns, Li equals averag*e length of 
one turn of the magnetizing coil in feet, E equals pressure 
in volts. 

Take the Edison machine shown in Fig. 28. Suppose 
it is a 220-volt motor. It is found that 11,074 ampere turns 
should be produced by each coil to force the desired flux 
around the circuit. 

Let us assume that the coil will be two inches thick. 
It is not good practice to make theru much thicker than 
this, because if they are the heat cannot get away from the 
inner layers out to the air through the outer layers. This 
makes the average length of the turn the circumference 
of a circle 10 inches in diameter, or 31.41 inches long, or 
2.62 feet long. 

E equals 110 volts, for the motor works on a 220-volt 
circuit and is provided with two coiJs connected in series. 

11.5x11074x2.62 

A equals equals 3040 

110 

Exanjination of Table I shows that this is between No. 
15 and No. 16 wire, and we will select No. 15 as being the 
size required. If it is desired to know just what number 
of a. t. No. 15 will produce, find how many turns one pound 
v^all make, or 101.63 divided by 2.62, or 38.8 turns per pound. 

A one-pound coil will have a resistance of .32 ohms per 
pound, and a coil made of a single pound will allow 110 
divided by .32 or 344 amperes to pass. The ampere turns 
of this size will then equal 38.8 x 344 equals 13,347 ampere 
turns. 



106 

It should be carefullj^ kept in mind that the amount of 
wire on a coil simply determines whether it shall run cool 
or hot; the size of the wire determines the number of am- 
pere turns. 

The formula is arranged on the assumption that the 
average temperature of the magnetizing coil is 125 degrees 
Fahrenheit. This assumption gives a larger wire than 
would be necessary if the coil operated at a lower tempera- 
ture./ because the resistance of copper wire increases .21 
of one per cent, for each degree Fahrenheit rise in tem- 
perature, and if the magnetizing coil couJd operate at an 
average temperature of 75 degrees Fahrenheit instead of 
125 degrees, the resistance of the coil would be 10% per 
cent, less, and its magnetiziijg power lO^o per cent, greater. 
If, however, the average operating temperature of the 
coil is above 125 degrees Fahrenheit, the size of the wire 
vnl] be too small rather than too large, because the resist- 
ance of the v>dre composing the magnetizing coil will be 
greater than that assumed in the formula. 

Wire enough should be put on the coil so that the 
watts lost will not be over .8 per square inch, and much 
more satisfactory results will be obtained if enough are used 
so that only .5 watts will have to be radiated per square 
ii^ch. 

In the coil for the Edison dynamo the radiating surface 
is 10 inches x the circumference of a circle 12 inches in 
diameter, or 10x37.64 equals 376.4 sq. in. While a large 
part of the heat radiated from the coil will escape from the 
outside, almost as much will be radiated from the ends of 
the coil and into the iron core inside. The iron core will 
conduct the heat to the heavy pole piece and yoke, where 
it is quickly radiated. 



im 



It is safe to allow three-fourths as much radiating sur- 
face for the rest of the coil as it has direct radiating sur- 
face, so the total radiating surface is 376-j-%(376) equals 658 
square inches. At % watt per square inch we have wasted 
in this coil 329 watts, and at 110 volts this means a current 
of 329 divided by 110 equals 3.0 amperes. 

We have seen that if the coil has only one pound of 
wire 344 amperes will flow. If only three amperes are 
wanted, we will have to make the coil weigh 344 divided by 3 
equals 115 pounds. The final result as to the winding for 
the magnetizing coil for the Edison dynamo is then 115 
pounds of Xo. 15 B. & S. wire. 

The next question is, will the space allowed for the 
winding take so much wire as this? 

The cross section of the coil was 2 inches x 10 inches and 
the average length of each turn was 2.62 feet. The number 
of turns in each layer would be 10 inches divided by .065, for 
No. 15 wire is .057 under the insulation and will be about .065 
over the insulation if single cotton-covered wire be used. 

10 divided by .065 equals 153 turns per layer. 

The number of layers will be 2 divided by .065 equals 31. 

The number of feet on the coil -will be 153x31x2.62 equals 
13.427 feet. 

Table No. 1 shows that single cotton-covered magnet 
wire weighs 10.13 pounds per 1000 feet, and 12,427 feet will 
weigh 12.43x10.13 equals 126 pounds. We can get in 126 
pounds of wire in the space that 115 pounds should be put in. 



108 



What sized wire and how much should be used to wind 

the ironclad dynamo shown in Fig. 31. Here the ampere 

turns required are 2791; the 

coil was 3 inches wide x 2 

inches thick. The average 

length of this coil may be 

found from Fig-. 44. The aver- 

6|- 




^ 






age length of the turn is 

6 plus 21/^ plus 6 plus 2y/plus 

(3.1416x5) 
or the circumference of a cir- 
cle 5 inches in diameter equals Dimenslons^oTmfg^Detizing coil- 
32.7 inches equals 2.72 feet. average length of turn. 

Suppose this is to be a 500- 

volt motor, then each of the two coils will be exposed to 250 
olts. 

Substituting in the formula, we have: 



11 V. X 2789 X 272 



A eouals 



250 



equals 337.8 



or 



a little larger than No. 25. 

Xo. 24 will have to be used. 

No. 24 or .020 wire has 819.2 feet per pound, and 819.2 
divided by 2.72 equals 301 turns per pound. Also it has 21 
ohms per pound and a one-pound coil allows 250 divided by 
21 equals 12 amperes to pass; 12x301 equals the ampere 
turns of No. 24 wire equals 3612. 

The coils for this motor are wound on forms and 
slipped over the pole piece. This allows all the outside and 
both sides to rarJiate heat, and we may allow one-half the 
inside surface of the coiJ as a radiating surface. 



109 

Radiating surface equals (32.7x2x2)-f(39x3)+y2 (26.5x3) 
equals 288 square inches. At i/o watt per square inch the 
current will be 144 divided bj^ 250 equals .58 amperes. 

If a one-pound coil passes 12 amperes, the coil must 
weigh 12 divided by .58 equals 20.6 pounds to cut the current 
down to .58 amperes. 

The winding- for the magnetizing coil for the motor in 
Fig. 25 for 500 volts is 20.6 pounds of No. 24 wire. 

It is clear that in a coil exposed to a constant potential 
the size of the wire and not the amount of wire or number 
of turns is what determines the magnetizing power. 

In a constant current dynamo, such as one used for arc 
lighting, the number of turns determines the magnetizing 
power, and the size of the wire simply -determines the 
amount of heating or the energy wasted in the coil. 

In a coil using constant current it is only necessary to 
divide the number of ampere turns required by the number 
of amperes. This gives the turns required. Then select a 
wire of such size that the coil will not g-et too warm. 



o 



The same rule should be followed in calculating the size 
of wire required for the series coil of a compound wound 
dynamo. It should he kept in mind that the heating of a 
shunt coil on a constant voltage raises the resistance and 
prevents more current from flowing, thus tending to pre- 
vent the coil from over-heatmg. 

In the series coil the reverse is true, for the heating of 
the coil makes the resistance higher and so increases the 
heating with a given current. 



J 



QUESTIONS FOR CHAPTER VIII, 



1. In calculating the ampere turns for a magnetizing- 
coil of any given size of wire, what is the first thing neces- 
sary to know about the dimensions of the coil? 

2. Describe how the number of ampere turns that will 
be produced by a coil of given dimensions and size of wire 
may be determined. 

3. How many ampere turns will be produced by a ceil 
whose average diameter is 10 inches, size of w^ire No. 20, coil 
exposed to an electro-motive force of 110 volts? 

4. What size of wire will be required to produce the 
same number of ampere turns as in pre<ieding question at 
271/2 volts? 

5. How many ampere turns wall be produced in a coil 
having an average length of turn of 4 inches if the voltage 
used is 110 and the wire used is No. 20? 

6. Why is it advisable when only a small amount of 
electrical energy is available for the purpose of magnetizing 
a small horse-shoe ma^-net to make the coil long and thin? 

7. Why are such large magnet cores used in commer- 
cial dynamos? 

8. When a coil is exposed to a constant electro-mo'tive 
force why does the size of the wire and not the amount of 
the wdre in the coil determine the ampere turns produced 
by the coil? 

9. Is there any reason for using a coil of considerable 
weight rather than using one weighing only a few pounds? 



Ill 



10. What size of wire will be required on the motor 
shown in Fig*. 31 for a six-volt plating dynamo; for 110, 220, 
and 500-volt motors? 

11. What weight of wire will be used in the coils cal- 
culated in the preceding question if 1/2 of ^ watt be radiated 
for one square inch of the surface of the coil? 

12. How many watts per square inch is it safe to allow 
the coil to radiate? 

13. Why is it not advisable to use a coil more than two 
inches in thickness? 

14. How much does the resistance of copper wire in- 
crease on account of the increase of the temperature? 

15. How is it possible to determine the number of 
pounds of wire that will be required in a coil to reduce the 
current consumed to a given amount? 

16. Calculate the size and weight of the wire required 
for a 250-volt motor of the dimensions calculated in answer 
to question 19, chapter V. 

17. Calculate the size of wire and weight required for 
the magnetizing coils in Fig. 31, provided they radiate y^ 
watt per square inch when used as a 250-volt dynamo. 

18. How are the ampere turns for a series coil calcu- 
lated? 

19. What is the effect on the power wasted in a coil 
of the raise in temperature in a coil exposed to a constant 
voltage? 

20. What is the leffect in a coil through which a con- 
stant current flows? * 



CHAPTER IX. 

WINDING ELECTRIC MACHINERY FOR DIFFERENT 

E. M. Fs. 



It was explained ?n Chapter IV that E. M. F. is pro- 
duced by a wire cutting lines of force, and it was also stated 
that where mag*netic line^ are cut at the rate of 100,000,000 
j)er second, one volt is produced. Fig*. 45 shows the cut- 
ting of the lines of force in a Gramme ring- armature and 
also the path of the lines. Fig-. 40 shows the cutting- in the 
internal bi-polar machine shown in Fig. 31. 



- r^ 


® 




J 


N 




1 
1 
1 

i 


S 






S; 


/ 



• Figure 45 
Production of E. M. F. in Gramme ring armature. 



113 



In the gramme ring armature the lines cross the air 
gap and pass around the ring from theN. pole to the S. pole. 
When the armature revolves, there is a constant movement 
of the magnetism in the armature. A few of the magnetic 
lines leak across the space inside the ring, as shown in the 
sketch. 




Figure 46 
Production of E. M. F. in drum armature. 



By applying the rule on page 47, w^e see that the cur- 
rent tends to flow toward the observer in the wires in the 
air gap in the lower part of the armature. 

The same rule shows that the current flows away from 
the observer in the upper part of the armature. A little 
thought will show that if the winding on the ring is a con- 
tinual spiral, these two currents will meet each other at 
points marked -\- and — about half way between the poles. 

If the spiral be connected at regular intervals to the 
bars of a commutator and two brushes touch this commu- 
tator at points on a horizontal line, there will be an E. M. F. 
between these two brushes equal to the sum of the E. M. F.'s 
produced in all the wires under one pole. 



114 

Suppose the armature revolves 1200 turns per minute; 
this vrill be 1200 divided by 60 equals 20 
revolutions per second. Also suppose there are 
1,000,000 lines of force flow^ing from the X. pole into 
the ring through the ring into the S. pole. Each 
vrire on the armature vrill cut 20 times per second the 
1,000,000 lines in the upper air gap, and therefore each vrire 
cuts 20x1,000,000 equals 20,000,000 lines per second. 

Since it requires cutting at the rate of 100,000,000 per 
second to produce one volt, each vrire on the armature pro- 
duces 

20,000,000 

equals 1-5 



100,000,000 



of a volt in passing through the upper air garp. The same 
wire produces the same voltage in the opposite direction in 
its passage through the lower air gap, but the two halves 
of the armature are in parallel. The E. M. F. produced may 
be illustrated by the diagram in Fig. 47. 




Figure 47 

Production of E. M. F. in an armature illustrated by two groups 

of batteries placed in parallel. 



115 



In Fig. 47 if each cell produces two volts, the whole 12 
cells produce only 12 volts, but the capacity for delivering 
current is doubled. The same thing is true of the dynamo 
armature. There are always two voltages produced which 
are placed in parallel. This fact makes the carrying capac- 
ity of an armature for current always equal to twice that 
of a single wire of the size the armature is wound with. 

If there are 550 wires or 550 turns on the armature in 
Fig. 41, the E. M. F. produced will be 550 times that pro- 

550 
duce in one wire, or equals 110, or, in the form of an 



equation: 



1,000,000x550x20 

E. M, F. equals equals 110 

100,000,000 

In symbols this becomes: 

NxTxS 

E. M. F. equals (11) 

100,000,000 

Transforming (11) to get the other quantities: 

E. M. F. X 100,000,000 

N equals — '■ (12) 

TxS 

E. M. F. X 100,000,000 
T equals (13) 

NxS 

E. M. F. X 100,000,000 

S eouals (14) 

NxT 



116 

Where N equals total number of lines flowing across 
one air gap, T equals total number of wires on the armature 
that cut lines of force, and S equals num'ber of revolutions 
per second. 

The turns on the inside of the Gramme nng do not cut 
any lines and so produce no E. M. F. 

In the case of the drum armature, however, the one 
side of a turn is in one air gap and the other side is in the 
other air gap. Therefore it is only necessary to have half 
as many turns in a drum armature to get the same E. M. F. 
as are required in a Gramme ring. At first sight it would 
seem that the Gramme ring would require much more wire 
for the same E. M. F. than the drum armature, but each 
turn is much shorter in the Gramme ring than in the drum 
armature. 

A very important practical advantage that the Gramme 
ring possesses is that the wires do not cross 
each other at the end of the armature. If 
anything is the matter with one doil in a Gramme ring 
it can be removed without touching any of the other coils. 
This is not the cale with a drum armature, for coils cross 
each other and it may be necessary to take off all the coils 
in order to get down to the one that is damaged. 

It is easy to see that with a given iron frame and arma- 
ture core the only thing necessary to do to make it develop 
different voltages is to put different numbers of turns on 
the armature. If it w^as desired in Fig. 45 to produce 220 
volts, it would be necessary to wind on 1100 turns of wire 
instead of 550. 



117 

Suppose there is a flux of 1,200,000 lines in the core 
shown in Fig*. 46, that there are 40 coils on the armature, 
that the machine runs 1,500 revolutions per minute. How 
many turns will it be necessary to use for 500 volts, for 220 
volts, and for 110 volts? 

Substituting in (13) 

500x100,000,000 

T equals 

1,200,000x25 

Solving- this equation, 

500x100,000,000 

T equals equals 1667 

1,200,000x25 

This is the number 'of active comduotors on a Gramme 
riaig' or drum arpiature. This will be ihlalf the number of 
turns on a dl'um armaiture. The number of turns will be 
1667 divided by 2 equals 834, and since there are 40 coils, 
each coil will contain 834 divided by 40 equals 21 wires. 
Each turn in such a coil contains two wires that generate 
E. M. F. 

The fundamental fact on which the action of the d;^Tia- 
mo depends was illustrated in Fig. 20, and it is excellent 
practice to determine from the direction of rotation of an 
armature and from the polarity of the magnet in any actual 
dynamo the direction in which the current is running on 
the armature. 

It is easy to determine the number of lines of force that 
are .lowing across any dynamo armature. 



118 



Suppose an Edison dynamo has 60 coils having- two 
turns each, and that it generates without any load 230 volt« 
at a speed of 1200 revolutions per minute. What is the flux 
across the armature? 

In this case 

S equals 1200 divided 'by 60 equiails 20. 

T equals 60x2x2 equals 240. 

Substituting- in (12), 

230x100,000,000 

N equals equals 4,792,000 

240x20 

In practice the only difference in dynamos desig-ned for 
the same output at different voltages is the difference in the 
number of turns of wire on the armature. 

Suppose the dynamo is designed for 500 volts with a 
certain number of turns on the armature; for 250 or 220 
volts only half this number is used and for 125 or 110 volts 
only one-fourth as many are used. 

Another way in which the voltage produced in a djma- 
mo may be considered is the change in number of lines of 
force enclosed or embraced by a coil. 

There will be an E. M. F. generated in a coil propor- 
tional to the rate of c*hainge in the number of lines of force 
embraiced by the eoil. 

If lines of force are put into or taken out of a coil at 
the rate, of 100,000,000 per second, one volt is produced. 
The E. M. F. produced by such a -change in the number of 



119 



lines embraced by a coil may be determined by Lentz law. 
According- to Lentz law the current produced in a closed 
coil by a change In the number of lines of force is a^lways 
in such direction as to oppose by its own magnetic action 
the change in number of lines enclosed. 

The result is, that when a S. pole is caused to approach 
a closed coil the current in it will flow in such a direction 
as to produce a S. pole in the coil, opposing the approach- 
ing* S. pole, and, when the S. pole is being* withdrawn, the 
current will flow so as to produce a N. pole in the coil op- 
posing the approaching N. pole. 

In the first case the approaching pole is repelled, and 
in the second, the receding pole is attracted; therefore 
power is required both to cause the pole to approach and 
to recede. 



QUESTIONS ON CHAPTER IX. 



1. How many lines of force is it necessary for a wire to 
out per second in order to produce one volt? 

2. Explain the production of electro-motive force in a 
g*ramme ring' armature. 

3. What is the office of a commutator on a direct cur- 
rent machine? 

4. Why is the resistance of an armature never more 
than one-fourth that of the vrire with which the armature 
is wound? 

5. How many volts will be produced in a two-pole ar- 
mature drum wound having 30 slots in the armature if the 
armature is wound with 30 bobbins of 10 turns each and the 
ilux across the arm'ature is 1,000,000 lines and the speed is 
1,200 revolutions per minute? 'How fast would the above 
armature run as a motor on a 150-volt circuit? 

6. Give from memory the four formulae expressing the 
relation between the E. M. F., magnetic flux, the speed and 
the number of turns. 

7. A bi-polar dynamo runs 1,140 revolutions per minute 
and produces 114 volts; there are 36 slots in the armature, 
each bobbin has six turns of wire. What is the magnetic 
flux across the armature? 

About .050 insulation should be used between the wire 
and iron. 



121 

8. A bi-polar motor on a 120-volt circuit is desired to 
run 1,100 revolutions per minute; there are 48 slots in the 
armature and the flux is 2,100,000 lines. Each slot in the 
armature is ^4 inch wide and % of an inch deep. How 
many tnrns will be required in each bobbin and what will 
be the resistance of the armature? 

9. What is it necessary to change about a motor in 
order to make it operate on a circuit of double its voltage? 

10. What is true of the number of turns of wire re- 
quired to produce the same electro-motive force on a 
gramme ring and a drum armature? 

11. What advantage does the method of winding used 
on a gramme ring armature possess? 

12. A bi-polar gramme ring armature is designed to 
run at 1,500 revolutions on 250-volt circuit; there are 56 
sections on the armature, each with two turns. What would 
be the section required in the pole pieces of this dynamo if 
a flux of 40,000 lines per square inch is used? 

13. Why will the resistance of an armature be quaaru- 
pled if it is rewound to run at half its original speed? 



CHAPTER X. 



COUNTER ELECTRO-MOTIVE FORCE. 



Whenever an armature is revolved in an excited field, 
E. M. F. is produced, w^hatever be the cause of the rotation. 
The armature may be revolved by a belt from an engine, 
or it may be revolved by a motor directly connected to it, 
or it may be revolved by a current flowing through it in 
such a direction that it becomes a motor. 



|C=^ 




WSsJ 



lH|l|l|l|l|l|lll[lllll|l|l|l|l|lll|||ill^ 



Fignre 48 
Illustration of the identity of counter and primary E. M. F. 



L. 



123 

In the first two cases the E. M. F. produced may be 
measured and used to produce current in an outside circuit 
if desired. In the last case, however, the E. M. F. appears 
as an E. M. F. opposing the E. M. F. of the current that 
drives current through the motor. This E. M. F. is called 
counter E. M. F., because it acts counter to the primary 
or principal E. M. F. That this counter E. M. F. really ex- 
ists may be made clear by a study of Fig. 48. 

In Fig. 4S the source of power is a turbine water wheel 
having a capacity of 100 H. P. This drives a shaft on which 
is a pulley that drives a 175 H. P. d3'namo for street railroad 
work. Connected to the shaft is a 75 H. P. dynamo that 
charges a storage battery. The average load on the street 
railway generator is 100 H. P., but it varies from 25 H. P. 
at the lowest to 175 H. P. at the highest. If the main dyna- 
mo is taking at any time 75 H. P., the turbine wheel will 
rise in speed a little and so raise the speed of the motor 
dynamo a few revolutions until the extra 25 H. P. is used in 
producing current that charges the storage battery. 

If, now, two or three cars all start at the same time, the 
load on the main dynamo may become 150 H. P. This will 
cause the speed of the turbine wheel to drop a little until 
the voltage of the dynamo is a little less than that of the 
storage battery, when current will flow from the battery 
into the armature of the machine, which is now a motor 
until it is developing 50 H. P. 

The electro-motive force of the dynamo now appears as 
counter E. M. F., which tends to prevent the storage battery 
current from flowing through it. • 

The scheme here illustrated is practical, and a variation 
in speed of 40 or 50 revolutions in 1200 would change the. 



124 



machine from a dynamo charging the storage battery at 
the rate of 75 H. P. to a motor taking power from the bat- 
tery and delivering 75 mechanical H. P. 

It is r,ow easily seen why a current in magnet of start, 
box is so nearly constant in speed. 

The resistance of the armature is very low, so that with 
full load current only a few volts are lost due to resistance, 
and the force that prevents a great rush of current through 
the armature is the Counter E. M. F. of the armature. Con- 
sider equation (14): 

E. M. F.xlOO,000,000 
S equals • 

NxT 

This indicates that the speed depends on the E. M. F. 
and will change in the same ratio that it does, for >J, the 
total flux through the armture, will remain constant as 
long as the voltage on the exciting coils does not cliange,and 
T, the number of turns on the armature cannot be changed 
after the armature is wound. 

The counter E. M. F. plus the volts lost in the armature 
must always be equal to the applied E. M. F., and if the 
resistance of the armature is low, so that onl}'- tw^o or three 
volts are lost in it at the heaviest load, the counter E. M. F. 
must remain constant, and if the counter E. M. F. is con- 
stant, the speed must remain the same. 
•> 

Looking at this in another way, the voltage forcing 
current through the armature is the difference between 
the applied and the counter E. M. F. 



If a heavy load is thrown on a motor that requires a 
heavy current, the first effect will be to reduce the speed. 
Reducing the speed lowers the counter E. M. F. and this 
causes a greater E. M. F. to iorce current through the arma- 
ture. 

If the applied E. M. F. is 110 volts and the resistance is 
.01 ohm, and the current required to run the armature with- 
out any load on it is 6 amperes, the counter E. M. F. is 109.94 
volts. If full load is thrown on, which may be' 100 amperes, 
the loss of voltage in the armature is one volt and the coun- 
ter E. M. F. is 109 volts. These figures are about what ob- 
tain in practice. Thus by a change of less than 1% in speed 
the motor has taken its full load current. 

In a shunt wound motor the field is constant and the 
speed is consequently almost perfectly constant. In a series 
motor, however, the current that supplies the armature and 
fields is the same, and anything that alters the current in 
t.he armature alters the current in the field and changes 
the flux through the armature. 

Figs. 49 and 50 show a diagram of the winding of a 
shunt and series motor respectively. 



I- ^" 

*■ ^ — - 



Figure 49 
Diagram of connections of shunt motor 



125 



In the shunt motor the amount of current passing 
through the armature does not directly affect the amount 
of magnetic flux which passes through the armature. In 
the series motor, however, the -amount of current passing 
through the field coil is directly proportional to the load on 
the motor. Since in a general way the amount of magnetic 
flux through the armature is proportional to the magnetiz- 
ing power of the field coil, the heavier the load on the motor 
the greater the magnetic flux, and consequently from equa- 
tion (i-i) the speed drops on account of greater magnetic 
flux. 






Figure 50 
Diagram of connections of series motor. 



Another thing which causes the speed to drop is the 
v^oltage lost in the resistance of the field coil and armature. 
Due to these two causes the speed of the series motor ia 
exceedingly variable, being high when the load is light apd 
the magnetic flux is small, and low when the load is heavy 
and the magnetic flux is great. 



127 

Equation (14) put in another way says that the product 
Df the. speed and the magnetic flux must always be a con- 
stant quantity as long as the E. M. F. of supply does not 
change. Consequently, when one of these two quantities 
(speed and magnetic flux) is large, the other must be smalL 

When constant current is supplied to a series motor the 
speed of the armature will tend to become very high and 
means must be provided for either weakening the field or 
rocking the brushes so as to prevent tcwD great a rise in the 
speed of the armature. 

The old "Baxter arc motors used the first of these meth- 
ods of controlling the speed, and the Brush arc motors 
used the second. 

The transmission of power by constant current machin- 
ery has been, however, almost entirely abandoned and con- 
stant current arc dynamos are not nearly so much used as 
formerly. The constant potential system having taken its 
place very largely, even for arc lighting. 



QUESTIONS ON CHAPTER X. 

:*, What is counter eleotro-motive force? 

2. Is there any difference between the counter electro- 
motive force produced in a motor and the E. M. F. produced 
in a dynamo? 

3. Why will 110 volts force only a few amperes through 
an armature when it is runmn-g having a resiistance of 1-100 
of an ohm? 

4. How may the flux through a motor armature be 
measured by the speed of the armature? 

5. A bi-polar motor armature has 66 slots; each coil 
has thre^ wires; the flux through the armature is 3,600,000 
lines. What will be the speed of the armature on 220 volts? 

6. If the speed of the armature should be 1,050 revolu- 
tions, what would the flux be? 

7. Why does the speed of a motor increase as the field 
coils get warm? 

8. Give another instance beside that in the text of the 
identity of ordinary and counter electro-motive force. 

9. What makes the shunt motor constant in speed, 
even under greatly varying loads? 

10. Why does the speed in a large armature change 
less with change of load than in a small armature? 

11. Why does rocking the brushes to an extreme back- 
ward position raise the speed of a motor? 



129 

12. A two-horse power armature "has a resistance of 
8-100 of an ohm; it is designed to run on 80 volts; one am- 
pere is required to run it at no load; at the heaviest load 
it is designed to take 30 amperes. What would be the drop 
of speed in per cent.? 

13. Why does the speed of a series motor vary so great- 
fy with the load? 

14. Why does the speed of the series motor change so 
much less with the load after the iron becomes saturated? 

15. Why is the speed of a 500-volt shunt motor with 
unsaturated magnetic circudt almost as high when running 
on 110 volts as on 500 volts? 

16. How will the speed of a compound wound motor 
vary ? 

17. As long as the magnetic circuit is unsaturated, why 
is the torque of a series motor proportional to the square 
of the current? 

18. To what is the torque of a shunt motor propor- 
tional? 

19. Why does the speed of a series motor tend to be- 
come excessively high? 

20. How is the speed of constant current motors gov- 
erned ? 



r 



CHAPTER XI. 



HYSTERESIS AND EDDY CURRENTa 



When iron is magnetized it tends to retain its magnet- 
ism, and when the direction of the magnetization is re- 
versed pow»?r is required to affect this reversal. 

Hysteresis may be called molecular friction caused by 
a reversal in positon of the minute molecular magnets of 
which the iron is supposed to be constituted. If the core 
of an electro-magnet should be composed of hard steel fil- 
ings and the direction of current through the magnetizing 
coil should be reversed, it is clear that there w^ould be an 
effort on the part of the steel filings to twist around end 
for end and in doing so there would be more or less fric- 
tion. Something of this same sort takes place when the 
direction of magnetization in a piece of iron takes place. 
It is easy to see that the direction of magnetization in l 
bi-polar motor armature changes twice every revolution. 

An examination of Fig. 31 \\ill show that if the left- 
hand pole be a north pole the magnetic lines will flow 
through the bottom of the teeth on tlie left-hand side of 
the armatdre from the top of the teeth to the bottom, and 
on the right-hand side of the armature from the bottom of 
the teeth to the top, but when the armature has made a 
half revolutiofn the direction of the magnetic lines will be 
reversed in any particular tooth. 



1^ 



131 



Table No. 9 gives Ithe loss in waitts per cubic foot at a 
speed of 1,200 revolutions per minute in a bi-polar field with 
various magnetic fluxes per square inch. This table is for 
g-ood soft wrought iron and the hysteresis loss in the iron 
of which ordinary armatures are made, is probably higher 
than that given in the table. 



TABLE No. IX. 



HYSTERESIS IN SOFT IRON. 

Lines uer sn in ^^"^ wasted per cu. ft. at 1200 

Lanes per sq. in revolutioDS per miuute in 

two-pole dynamo. 

25,000 73 

30,000 108 

35,000 130- 

40,000 155 

45,000 . 182 

50,000 216 

55,000 238 

60,000 275 

65,000 ^ 314 

70,000 348 

75,000 395 

80,000 431 

85,000 472 

90,000 512 

95,000 564 

100,000 520 

105,000 670 

110,000 780 

115,000 964 

120,000 1124 



132 



It will be noted that in a four-pole field the directiov 
of magnetization is reversed twice in every revolution, and 
if the armature in a four-pole machine runs at the same 
speed that it does in a two-pole, the loss by hysteresis will 
be twice as great with the four-pole machine as with the 
two-pole. 



EDDY OR FOUCAULT CURRENTS. 



It is clear that there is the same tendency to produce 
current in the iron part of the armature due to the cutting 
of the magnetic lines as there is in the copper wire which 
is wound on its surface. Ji in Fig. 31 the iron core was 
solid, there would be a very large current circulating in 
the iron core in the same direction as that which flows 
through the wire^ in the air gap. Such a current as this 
would be entirely useless and, worse still, would heat the 
armature core very hot; consequently, the armature, in- 
stead of being solid, is built up of thin sheet iron discs. 

These discs carry the magnetic lines without difficulty 
and an armature built up of these discs has the same mag- 
netic properties as a solid wrought iron armature would 
have. 

Fig. 51 shows the direction in ^vhich the currents tend 
to circulate around the armature, land show^s how these cur- 
rents are prevented from flowing by the ins>ulation between 
the discs. 



133 



The discs in Fig*. 51 may be insulated with paper, but 
la practice it is found that the thin coasting- of ox^de on 
the outside of each disc is enoug^h to accomplish the same 
purpose and produces an armature which will always re- 
main as solid as when first put up. The use of paper be- 
tween the discs is dangerous, because in time the paper 
charrs and crumbles to pieces, leaving the discs loose. The 
best way to treat the discs is to give them a thin coating of 
linseed oil; this forms a surface having the same insulating 
properties as paper, and the heat -to whiioh the armature as 
subjected will not affect it. In practice the discs for arma- 
tures run from ten to twenty-five thousandths of an inch in 
thickness. Even in the thinnest disc there are small eddy 
currents circulating which take power to produce and which 
heat ihe armature core. The loss by eddy currents is 
proportional to the square of the speed at which the arma- 
ture is run, because at double speed, other things being 
equal, the E. M. F. is twice as great, and this double E. M. F. 
produces double current. 




Figure 51 

Circulation of eddy currents 

stopped by lamination of the iroxi. 



134 

Formula 8 shows that the loss in watts with double 
volts and double current is four times as great as with the 
given voltage. It is because of the loss by eddy currents 
that would occur with solid pole pieces that pole pieces are 
laminated. A consideration of the way in which E. M. F. is 
produced shows that when the number of lines of force en- 
closed by circuit is changed there is an E. M. F. produced 
which tends to send current around the circuit in such a 
direction as to oppose the change. 

When an ironclad armature with a short air gap is re- 
volved the magnetic lines flow from the pole piece into the 
armature in tufts or bunches. These bunches of lines pass 
across the pole piece with the motion of the armature and 
set up currents in the solid pole piece. It is possible by the 
use of a long air gap to cause the lines to flow from the pole 
piece uniforml3\ But vv'ith short air gaps it is necessary to 
laminate the pole piece in order to get rid of eddy currents. 
(See Fig. 33). 



QUESTIONS ON CHAPTER XI. 



1. What is nysteresis? 

2. What would be the difference in passing an alternat- 
ing- current and a direct current around an iron core ajs far 
as hysteresis is concerned? 

3. Why is the hysteresis in a four-pole motor (twice as 
great as in a two-pole? 

4. Why is there hysteresis in a revolving* armature? 

5. What are eddy currents? 

6. In what diirection would the eddy currents tendi to 
flow in the drum armature shown in Fig*. 46? 

7. Why is the iron in an armature laminated? 

8. Why are cables used on surface wound armatures 
instead of solid wires? 

9. Wliy does the pole piece of a motor get warm if an 
iron clad armature is used with too short an air gap? 

10. Why will the heating in such a case be much great- 
er with steel pole pieces than with cast iron? 

11. What will be the loss from the eddy current that 
flows clear around the armature in Fig. 31 »if the flux 
through the armature is 1,200,000 lines, the speed of the 
armature is 1,200 revolutions per minute, the resistance of 

the armature between end plates 1-10 of an ohm and the end 
plates are so large as to ihave a megligible resisitance ? 



136 

12. Is there* any difference in their nature between 
eddy currents and the useful current produced by an arma- 
ture? 

13. Why was paper formerly used between armature 
discs? 

. 14. Why has this practice been abandoned? 

15. In what way do the watts lost from eddy currents 
vary with the speed? 



CHAPTER Xn. 



ARMATURE REACTION. 




When a dynamo produces current these currents flow 
around the armature in such a direction as to magnetize 
the armature at right angles to the main field magnets. A 
consideration of Fig. 52 shows this, and if the direction of 
circulation of current in Figs. 45 and 46 be worked out, the 
result will be the same. 

The position of the brashes 
en the commutator determines 
►There the current which flows 
through the armature shall enter 
and leave the armature, and so 
determines the direction of the 
polarity of the armature as an 
electro-magnet. If the brushes 
in Fig. 45 be moved around the 
commutator the point at which 

the current divides to pass around the two halves of the 
Gramme ring will move with it. It is clear that the pole 
of the armature will be at the point at which the current 
divides. The strength of the armature as an electro-ipagnet 
is directly proportional to the amount of current which is 
drawn from the armature. The practical ett'ect of the arma- 
ture becoming a powerful magnet is to cause more magnetic 
lines to pass into the armature at one side of the pole piece 



Figure 52 

Armature reaction in a 

dynamo. 




138 

than at the other, for a north pole in the armature wil] 
attract the lines from the south pole of the held and repel 
those from the north pole. When this action is sufficiently 
great, the axis along which the magnetic lines How is ro- 
tated so as to occupy a posifti'on between the polar- 
ity caused by the fields alone and that caused by the arma- 
ture alone. When the brushes are placed as in Fig. 52 mid- 
way between the north and south poles of the field, the 
only effect of the magnetization 
of the armature is to cause more 
lines to flow into the armature 
from the top of the pole ^ piece 
than from the bo^om. The teai'- 
dency is to rota'te the a:xis of the 
magnetic lines which pass 

throuo-h the armature. It does r>r. + ^^^^,. ,. 

Connter magnetic motive 

not directly tend to decrease the force of armature reaction, 
flnx of the lines through the ar- 
mature. As will be seen in the next chapter, it is necessary 
in order to stop sparking in a dynamo to 
rotate the brushes a short distance in the 
direction of the rotafioTi of the armature. This 
produces the oomdition of things shown in Fig. 53, in which 
the armature reaction is such as to directly oppose to some 
extent the passage of the magnetic flux through the arma- 
ture. It will be seen that if the brushes were rotated si^il 
further forward that the magnetism in the armature would 
still further oppose that of the fields. In arc dynamos the 
armature is made relatively a very powerful magnet and 
its magnetizing action is fully equal that of the fields. By 
rotating the brushes it is easy to see that the amount of 
magnetic flux w^hich would pass through the armature could 
be very greatly altered. In the Wood arc dynamo the regu- 



139 

lation is entirely effected in this way. In the Brush arc 
dynamo part of the current is shunted by or around the 
neld coils; this makes the armature relatively muc^h strong 
er than the fields, and the armature reaction prevents mag- 
netic flux from flowing- through the armature, as will be 
more fully explained in the chapter on sparking. 

When the field is relatively weak, with reference to the 
armature, it is necessary to rotate the brushes through a 
considerable arc in order to stop sparking; the rotation of 
brushes makes the effect of the armature reaction much 
greater than it otherwise wpuld be. In fact, if the brushes 
of a Brush arc dynamo be always rotated to such a position 
that the spark is the same length, it is necessary to reduce 
the current in the fields only from 9^2 to 7 amperes, to re- 
duce the flux through the armature from a maximum to 
zero. The armature reaction with 10 amperes is equal in 
magnetizing force and opposite to that of the fields with 7 
amperes. * 

If the brushes of a series. dynamo be rocked quite well 
forward in the direction of rotation and current be sent 
through the armature alone, the magnetizing force of the 
armature will set up a powerful magnetizing flux through 
the armature and fields; and, if the machine be run as a 
motor, it will operiaite as if Itlhe field coils were in ^aidtiilooi, 
with the exception that it will spark furiously. In this 
case the armature reaction furnishes the magnetic field. 

In ordinary constant potential dynamos and motors the 
armature reaction is a necessary evil, and the dynamo shoula 
be carefully designed so that the armature magnetizing 
force shall never reaoh more than from 1-2 to 2-3 the mag- 



140 

netizing power of the fields. That is, the ampere 'turns on 
the armature at full load should be from 1-2 to 2-3 the am- 
pere turns on the field at full load. 

As was noticed in Chapter IX, there are twice as many 
tarns tof wire required on a Gramme ring armature as on a 
drum armature -to produce the .same number of cfonduc- 
tors, in which the E. M. F. is set up by means of the rota- 
tion of the armature; that is, the same number o-f amperes 
produce twice as many ampere turns in a Gramme ring 
armature as in a d<rum armature of the same power. This 




Figure 54 
Flow of current in multipolar dynamo. 



© Indicates current flowing toward the observer. 
X Indicates current flowing away from the observer. 



141 

fact make the Gramme ring a superior armature [for arc 
dynamos where dt is desired to have the armature a pow- 
erful ma.gTiQt, 'and indicates that the drum armature is the 
better -armature for nonstant potential dynamos in which 
the armature reaction is to be avoided as much a<s possible. 
It is to reduce the effect of armature reaction that large 
constant potential dynamos are made multi-polar. 

Fig. 54 is the diagra>m of a siix-pole dynamo with a 
drum armature, and shows the direction in which the cur- 
rents in the armature flow. It will be seen that the number 
of turns under each pole may be made quite small, but that 
the number of ampe-re -turns required on the fields will be 
larger on the multi-polar machine than on the bi-polar, be- 
cause the area of iihe. air gap is relatively much smaller. 
The small number of turns on the arfmature and the largpe 
number of ampere turns required on the field make it pos- 
sible for the aiynature to carry very heavy currents, without 
allowing the number of ampere turns in the armature un- 
der each pole to become great euough to seriously distort 
the field. 



QUESTIONS ON CHAPTER XII. 

1. What is ar-mature reaction? 

2. On wbat does the strength of the arma;ture as a 
magnet depend? 

3. In wihat way is the armature m-agneti^ed with ref- 
erence to its field? 

4. Why is the pole piece whioh the armature is leav- 
ing in a dynamo magnetized more strongly than the oppo- 
site one? 

5. Why does -the movement of (the brushes affect the 
armature reaction? 

6. Why does armature reaction usually reduce the 
amount of flux? 

7. H-o^^ would the brushes have to be set in a dynamo 
to increase -the amount of flux through the armature? 

8. In wO^at kind of dynamos is it desirable to have ar- 
■natare reaction? 

9. How is the regulation of the Wood arc dynamo 
effected? 

10. How is 'the regulation of a Brush arc dynamo ef- 

feoted? 

11. How sbocld the brushes on a motor be set in order 
to dispense w^th the field coil? 

12. In Oonstant potential machinery, how strong is it 
best to make the magnetizing power of the armature at 
lull load wi-th reference to the fields? 



^ 



143 

13. Wliy is the Gramme ring* anexcellent form of ar- 
m'atfurie for a eonstamt current machine aind a poor form for 
a oonstanit poten'tdal machine as compared with a drum 
armature ? 

14. What device is used to prevent the effect of arma- 
ture reaction in larg-e machine's? 

15. With the siame mumber of turns on the armafture, 
how much will the farmarture reaction be reduced by chang- 
ing from "two to fooir pole? 



CHAPTER Xin. 



SPARKING. 



Intimately connected with armature reaction is the 
sparking" that occurs on the commutator of the direct cur- 
rent dynamo or motor. Every ordinary machine 
has a load at ^^^hjch it will spark. Consid- 
eration of Fig. 55 shows that the current is 
flowing through the coil in one direction just before 
it reaches the brush and is flowing through it in the oppo- 
site direction just after it leaves the brush. During the 
i'me that the coil is short circuited by the brush, the direc 
tion of the curreni: is completelj^ reversed. Fig. 55 shows 




Figure 55 
Comnmtation in Gramme ring armature. 



this in detail. Three coils are shown, a, b and c. In c 
the current is traveling through the coil in one direction; 
(he coil b is short circuited by the brush. In c the curreuc 
/s traveling through the coil in the oppos-ite direction tc 
that in a. 



145 

The currents in coils e and a are each equal tto half the 
total armature current. The current in the short circuited 
coil will depend ooi the magnetic field in which 
it is moving- while it is short circuited. If 
it is still under the influence orf the north 
pole which it is leaving, the current will immediately 
increase as soon as it is short circuited by the brush, and 
may continue quite large until it is about to leave the brush. 
Then the resistance in its circuit, due to the small surface 
of the brush which rests on the commutator bar, reduces 
it to zero. A current must now in a very small space of 
time increase in the coil b from zero to the full value of 
half the armature current. The self-induction of the coil b 
prevents this from being done and the commutator bar c, 
leaves the brush before the current in coil b has reached its 
full value. A short arc is now formed between the extremity 
of the brush and the bar c, w^hich lasts until the electro- 
motive force has overcome the self-induction of the coil b 
and raised the current in it to half the armature current. 
It should be explained here that the self-induction of a coil 
is of the same nature as inertia in a weight. The inertia 
tends to prevent motion from being imparted to the weight, 
but when once in motion the inertia tends to prevent the 
weight from coming to rest. 

The self-induction in a coil acts the same way with ref- 
erence to the electric current. It tends to prevent the cur- 
rent from being established in the coil, but, when once es- 
tablished, tends to prevent it from changing value or from 
dying out. 

The self-induction of a coil surrounding an iron core is 
very much greater than that of the same coil in the air; 
furthermore, the self-induction of a coil increases as the 
square of the number of turns in the coil. 



146 



We have traced the acttoin in the commutaftion of the 
coil b where the brush is rocked so far back in the direc- 
tion opposite to thait of rotaitdooi that the coil b is still cut- 
ting* the lines whion flo-w from the pole which it is leaving. 
Under these circumstances it is seen that tihe self-induction 
of the coil prevents the current froTQ being reversed until 
so late tha-t a small arc forms between the point of the 
C'ommurtator brush a.nd one oif the commutator bars to 
which it is attached. This continual 'arcing- is called spark- 
ing. When, however, the brush is rocked forward 'in the 
direction of rotation until 'the coil b is coitting the lines of 
force which flow from the lyole which it is 'approaching, 
the action is very different. Fig. 56 shows the relative 
position of the poles and the coil being commutated. 

When the brushes are rocked into the position shown in 
Fig. 56 the coil b is short circuited while it is cutting lines 
from the south pole, or the pole toward which it is ap- 
proaching. The E. M. F. generated in the coil b will be op- 
posite to that generated 
while the coil was under 
the influence of the north 
pole; therefore, as soon as 
the coil b is short circuited 
by the brush theE.M.F.set 
up therein tends to reduce 
the current in the coil to 
zero and next to generate 
a current in the coil to the 
reverse direction. If all the 
conditions are just right 

this current wHill be equal to half the armature current at 
the moment the bar c' leaves the brush. When these con- 




Flgure 56 

Diagram of correct and sparkless 

commutation. 



147 

ditions obtain, there is no possibility of any arcjng" between 
the commntator bars and the brush, and consequently the 
commutation is sparkless. It is necessary that the coil b 
should be in a field which will not tend to increase the 
current that is already flowing in it at the moment that the 
coil is first short circuited. It is clear that the exact con- 
ditions which would make sparkless commutation possible 
if sparkless commutation depended only upon magnetic con- 
ditions can only exist for one particular position of the 
brushes and one particular load on the armature. For, sup- 
pose the coil b were short circuited in a quite powerful field 
of the pole toward which it is approaching-, then a current 
flowing in it at the instant it was first short circuited would 
die out almost immediately and a large current would be 
sQt up in the opposite direcftion, amd woaild 'tend to increase 
until broken by the bar c, leaving the brush. This would 
produce an aire dua to over-commutaltion. 

A factor of very great importance in commutation 
is the resistance between the brush and the commutator 
baj's. It must be carefully kept in mind that while the 
current in the coil b is being reversed by the small E. M. F. 
generated in it, the main current of the dynamo is passing 
from the cammut-ator bars b, ajid c, to the brusih. There 
will therefore be a greater or less difference of potential 
between the bars b, and c, and the brush. This difference 
of potential or voltage wall depend on the resistance be- 
tween the brush and commutator bars and also upon the 
current. It is clear that if there should be a tendency in 
the coil b to over-commutate by being placed in too strong 
a south field, this local current must flow through, the leads 
c„ and b„ across from the bar b, tlirough the brush to the 
bair c, and to the ooil. In order to do this the current which 



J48 



naturally fjows from the bar b' into the armatufre will be 
increased. ^Vhile the current which naturally runs from 
the brush throug^h the lead or connection c'' to the arma- 
ture is reduced by the same quantity. This consideration 
w!ll show that there is very little danger of over-commuta- 
iion when the armature carries a fairly large load. 

The tendency of a considerable armature current trav- 
eling from the brush into the bars and so into-the armature 
is to immediately stop any current which might flow in 
the coil b, because the tendency is for the leads or connec- 
tions c" b" to carry the -same amount of current. And 
this tendency is increased if there is considerable resistance 
in the two leads c" and b". When these two leads are 
carrying the same amount of current it is manifestly im- 
possible for any local current to circulate in the coil b. As 
the bar c' moves away from the brush the resistance thait 
the current me^ts in flowing from the bar c' increases on 
account of the smaller surface of contact between the brush 
and the commutator bar c'. This tends to reduce the cur- 
rent in the lead c", but such a reduction of the current 
must be accompani 'l by a corresponding increase of the 
current in the coii ^, 

This is becauise the current dm the doiil b plus the current 
in the lead c" must -always equal h<alf the armature current, 
and anything that reduces the current through the lead c" 
must inci-ease the current through the coil b. ^ 

The resistance between the brush and the commutator 
bar c' thus powerfully tends to set up a current in the short 
circuited coil in the same direction that it will flow in the 
coil after it is completely commutated, because it tends to 



149 

prod lice an even distribution of current over the surface of 
the brush. 

As the har c* irecedes from the brush the resisitance to 
the passage of current to the left hand side of the armature 
b}' the path c' and c" increases, and this increases the ten- 
denc3^ of the current to flov^ through the coil b. When the 
bar c' has entirely left the brusih the current in the coil b 
will be equal to half the armature current, and in this way 
again sparkless commutation will have been attained. 

If the brush is of carbon instead of copper, the resist' 
ance between the bar an^ the brush will be very much 
greater with brushes of the same size. But even with a car- 
bon brush large enough to carry the current there will be 
from three to five times the voltage between the commu- 
tator bars and the brush that exists with a copper brush. 

A still more important factor in sparkless 
commutation is the more even distribution of 
current between the brush and ciommutator bars 
that the carbon brush imposes. The resistance of the car- 
bon is at least 100 times as great as that of a block of cop- 
per the same size, and therefore the tendency of the cur- 
rent to spread itself out evenly over the surface of the brush 
when passing from the commutator bars to the brush is 
very great. If this effect is great enough when the brush 
covers both commutator bars b' and c', fully 25 amperes will 
flow from each commutator bar to the brush, provided the 
armature is carrying 50 amperes (see Fig. 57). When the 
commutator bar c' has advanced so that only half its surface 
is covered by the brush, I214 amperes flow into the brush 
■^rom the commu«tator bar c' 25 a-mperes from the commuta- 
tor b', and 12^2 amperes from the commutaitor bar a', which 



150 



would by this time have half its surface covered by the 
brush (see Fig. 58.) ^At 'this instant the coil b would be 
carrying 12i/^ amperes into the left hand side of the arma- 
ture and would be, so to speak, three-quarters commutated. 
The coil a would be carrying 12yo amperes into the right 
hand side of the armature and would be, so to speak, one- 
quarrter commutated. As the commutator bar c' leaves the 
brush the current flowing from the brush into the commu- 
taitor bar c' will diminish umtil at the instant the bar 
leaves the brush it will be zero, and the current in the coil 
b will correspondingly increase until, at the instant the 
commutator bar c' leaves the brush, it will be equal ito full 25 
amperes, or one-half the armatuue current. At this instant 




Figure 57 

Current from armature 50 amperes. Current into bare', 25 am- 

I>eres and into bar b', 25 amperes. Current through iDOth 

c" and b", 25 amperes each. Current in coil b, 

none. Current in coils a and c , 25 amperes each. 



the brush would rest equally on the bars a' and h\ 25 am- 
peres would flow into each bar, 25 amperes would flow into 
each lead a" and b" and the current in the coil a w^ould be 
reduced to zero, or it would be half commutated (see Fig. 
59.) 

The objection to the copper brush is that the resistance 
between the copper brush and the commutator is ^o low 



151 



that the current can easily bunch up on one side of the 
brush; for instance, when the commu'tator bar c' had moved 
to such a position that only one-third of its -surface rested 
under the brush, the resistance of contact would be so low 
that the 25 amperes of armature current could easily flow 
into it. If this should be the case the current in the coil b 
would have to be built up almost instantly and a large cur- 
rent would flow from the tip of the brush into the com- 
mutator bar c' just as the bar was leaving* the brush. 
Enough current would flow, in fact, to fuse the very tip of 
the brush and bar at the edge of the bar, 
and the fused bit of copper would appear 
as copper dust thrown off from the commu- 
tator. This fusing action roughens the bars, which tends 




Figure 58 

Current from armature 50 amperes. Brush covers half bar e 

all of b' and half of a'. Current into bar c', 12>^ amperes. 

Current into bar b', 25 amperes. Current into bar 

a', 12}4 amperes. Current through coil b, 

12j^ amperes. Current through coil 

a, 12^ amperes. 

to make commutation still more imperfect. Trouble of this 
kind once started grows rapidly worse, until it is necessary 
to put on new brushes or to retrim them and to true up the 
commutator. The higher resistance of carbon makes it 
impossible for enough current to pass from the edge of the 



152 



copper bar to the tip of the carbon brush to fuse the copper. 
The action just described, viz: the distribution 
of the current over the surface of the brush 
is the most important one in the progress of 
commutation. The only thing which prevents this 
from always producing spairkless commufcatiKDoi is Ithe self- 
induction of the coil to be commutated. It is clear that if 
commutation is to take place easily this self-induction 
should be as low as possible. If three-tenths of a volt ap- 
plied for 1-100 of a second is sufficient to overcome the self- 
induction of a coil of one turn on a given armature, 1 2-10 
volts, or four times as much as would be required to over- 
come the self-induction and reverse the crrrent in a coil of 
two turns on the same armature. Nine times 3-10 would be 




Figure 59 

Current from armature 50 amperes. Brush covers all bars 

a' and b'. Current into bars a' and b', 25 amperes each. 

Current in coil a=0. Current in coil b=25 

amperes. Coil b completely commutated. 



required with three turns, and so on, for the self-induction 
of a coil on any given armattire is proprtional to, the square 
of the number of turns on the armature coil. 

It will be noticed that the effort to commutate the 
short circuited coil due to the resistance of the brush in- 



153 

creases with heavy loads; thus there is twice as much ten- 
dency for the ourrent to flow into the brusii eve«nly with 50 
amperes as there is witli 25. This gives us twioe the 
voltage for commutating the current in a sihort circuited 
coil when 50 amperes are flowing than is^aviailable when a 
current of 25 amperes is being produced by the armature. 
On the other hand, the commutation which is prt>duced by 
the short circuited coil cutting the lines of the field toward 
which it is approaching, grows weaker and less perfect as 
the load increases, because the increasing load increas.es 
the a/rraature reaction and the increased armature reaction 
weakens the field which the coiil is approaching, while 
strengthening the pole from w^hioh the coil is receding. 
TJierefore the commutation produced by the cutting of 
lines of force is strongest when it should be weakest and 
weakest when it sho<uld be strong^est. Since perfect com- 
mutation is obtained even under the most trying conditions 
it is clear therefore that it is produced madnly by the ten- 
dency to the even distribution of th-e current oai the brush, 
and not to the character of the fielcl in which the sihort cir- 
cuited coil is moving. In order to obtain the best results, 
or even good results, it is necessary that the codl while 
short circuited should not be to any extent under the m'^g- 
netic influence o^f the pole from which it is receding. We 
niay therefore sum up the requirements to good commuta- 
tion as follows: First, carbon brushes of sufficient width 
to give the coil time to reverse; second, low self-induction 
of the Sihort circuited coil, so that 'only a small E. M. F. 
need be applied in order to reverse the current in it; third, 
an armature in which the reacition is sufficiently small, so 
that the pole toward v^hich the sihort circuited coil is ap- 
proaching is noit very much weaker with the hea.viest load 

than with no load. 

11 



154 



The above description applies to the commutation in a 
dynamo. The same description will apply to the commu- 
tation in a motor, except that in order to obtain magnetic 
reversal of thje ooil the brushes muisit be rocked in a dir^ic- 
tion opposite to that of rotation so as to bring the short 
circuited coil under the influence of the pole which the 
short circuited coil is leaving instead of approaching, as in 
the case of the dynamo. 

A little thought will show that in the case of both dy- 
namo and motor it is necessary, in order to produce mag- 
netic commutation, to have the short circuited coil under 
the influence of the pole that is weakened by the armature 
reaction. 

Figs. No. 57, 58 and 59 show in three Qteps.the process 
of commutation in coils a and b. 



QUESTIONS ON CHAPTER XIII. 



1. 'What happens to the direction of flow of current in 
a coil in passing- a commutator brush? 

2. In a bi -polar armature how much current is passing 
through each coil? 

3. On what d-oes ^the current in tbe aoil lor oo^ls s^hjor^t. 
circuited bj- the brush depend? 

4. What is the effect of introducing resistance in the 
leads between the armature windiiig- and the commutator 
bar? 

5. What is the condition of sparkless commutation? 

6. What is the effect of self-induction in a coil? 

7. How much sparking would there be if self-induction 
could be entirely eliminated? 

8. Why is the sparking less in a dynamo and greater 
in a motor when the brushes are rocked forward in the 
direction of rotation? 

9. If nothing but magnetic conditions govern sparking, 
would it be possible to obtadn perfect commutation under 
all loads? 

10. What is over-commutation? 

11. How would you set the brushes of a dynamo* bo 
that it would spark less with a load than without a load? 

12. What other important factor is to be considered in 
commutation? 



156 

13. What is the effect of difference of potential be- 
tween the brush and commutator bars in co-mmutatiou? 

14. Why is over-commutation very unlikely to occur 
with considerable load on the armature? 

15. Why do carbon brushes prevent sparking? 

16. Why does the commutator run warmer with car- 
bon than with copper brushes? 

17. If means could be devised to cause the current to 
pass evenly from the brush into the commutator, what 
effect would this have on sparking? 

18. Why does the carbon brush approximate this con- 
dition more closely than the copper brush? 

19. ^^Tij^ does a brush whicOi covers two or three com- 
mutator bars work with less sparking than one which is 
very narrow? 

20. Describe the action of a carbon brush in producing 
commutation. 

21. Why is sparking usually accompanied by cutting 
of the commutator? 

22. If it is necessary to use a copper brush, whait must 
be true of the self-induction of the coils? 

23. What does the fact that motors may be run heavily 
loaded in both directions withouit sparking sLhiow as to tthe 
relative importance of the magnetic conditions and the 
brush design in producing sparkless commutation? 



CHAPTER XIV. 



WINDING OF DYNAMOS AND MOTORS. 



The office of the wire on an electric dynamo or motor 
is twofold: First, wire is used on the magnetizing coils to 
convey the current which causes the iron or steel cores to 
become electro-magnets. This winding should simply be 
disposed and connected up so as to force the magnetic flux 
around the circuit. If possible, it is always better to wind 
the magnetizing coil in the shape of a cylinder, for a circle 
includes the largest possible area with the smallest possible 
periphery. It is, of course, the object of the magnetizing 
coil to drive as many lines of force as possible through its 
interior; at the same time it is very desirable that the length 
of the average turn of the field wire should be as sniall as 
possible. Therefore it is always advisable to make the 
cross-sections of that part of the magnetic circuit around 
which the magnetizing coil is placed a circle or a square 
with the corners cut off, or, if a laminated pole piece is used, 
a square. The field winding should also be placed as close 
as possible to the air gap. This is to prevent as far as pos- 
sible magnetic leakage. 

The second object of the wire on an electric dynamo or 
motor is to crttj the current which passes through the 
armature. We will consider simply the case of the dynamo, 
for, as was pointed out in the chapter on "Electro-Motive 
Force," a dynamo and motor are perfectly similar machines. 



158 

and one may be converted into the other without the knowl- 
edge of an observer watching the machine in operation. 

In the case of the dynamo, E. M. F. is generated in the 
armature wires as they pass under the pole piece. An equal 
amount of E. M. F. is generated in each wire, and in order 
to get the best result these wires must be connected up into 
a series, so that all the electro-motive forces generated un- 
der a field pole shall be added together. 

When the winding is arranged so that this is accom- 
plished, the current will flow in all the wires under each 
pole piece in the same direction. Since the E. M. F. pro- 
duced under the north pole is opposite in direction to that 
produced under the south pole, it is further necessary to 
arrange the winding so that the current in all the wires 
under the north pole shall flow^ in one direction and the 
current in all the wires under an adjacent south pole shall 
flow in the opposite direction. 

A study of Figs. 45, 46 and 21 will make this clearer. 
Any armature winding which fulfills the above conditions 
will operate satisfactorily. Fig. 60 is a diagram of the 
winding on a two-pole drum armature. Here the end of 
one coil and the beginning of the next coil are brought 
down and attached to a commuitator segment. Suppose 56 
coils are used cm the armaiture and 56 bars in the commuta- 
tor, 'and four turns on each coil, and that th'e armatnre is 
of such diameter as to aocomimodate 56x4 equals '224 wires 
in a single layer. By the time 28 wires or 'leads are brought 
down to the »commutator the whole surface will have 
been covered with 'a layer of wfires. In order Ito bring down 
enough connections to All up the other half of Jtihe commu- 
tator, it will be necessary to wind on a second layer 



159 



of wires over the firsit layer. Xow between any 
two ordinary coils in either la3^er of the armature 
winding there will be only the diffe.rence of poten- 
tial or voltag-e that exists between two adjacent bars 
in the commutator. When the last coil is wound onto the 
first layer it will be seen that it lies alongside of the first 
coil that w^as pnt on, so that between the first and last coils 
that are put onto the layer of the armature we have the 




PigareeO 

Diagram of connection of bipolar armature, 
horizontal winding. 



A 



160 



full voltage which the armature is designed to carry. There- 
fore, while it is not necessary to insulate between adjacent , 
coils in the same layer, it is necessary to carefully insulate 
between the first and last coils that go on the same layer. 

A study -of Fig. 60 will furthermore sho^vv that there is 
in every pari of the armature the full difference of poten- 
tial of the armature between the upper and lower layers 
of wires. Therefore it is necessary to insulate ver}^ care- 
fully the upper and lower layers. A winding such as is 
shown in Fig. 60 is called a horizontal winding. If, instead 
of winding the four turns of each coil alongside each other 
in one layer, they should be wound with two turns in two 
layers a space would be left between the coils which are 
attached to adjacent bars on the commutator. This space 
may be tilled by winding in a coil which is connected to a 
bar on the opposite side of the commutator. 

Fig. 61 shows a diagram of this 
winding. It is to be seen that each 
coil must be insulated from its neigh- 
bor for the full dif^rence of poten- 
tial in the armture. This is called a 
vertical winding. Practically, a hori- 
zontal winding is less liable to trouble 
than the vertical winding, because it is 
easier to insulate the layers from each 
other than it is the vertical divisions 
between adjacent coils. 

It is possible to carry the leads 
connecting the armature winding and 
the commutator bars a quarter revolu- 
tion more or less around the armature if desired, 
in order to bring the position of the brashes into a more 




loO 

Figure 61 

Diagram of vertical 

winding for bipolar 

drum armature. 



161 



convenient location than they would have if the leads were 
brought out straight as shown in Figs. 60 and 61. 

In a four-pole machine two general methods of winding 
may be pursued, one is called a wave winding, the other a 
lap winding. In the wave winding there are only two paths 
for the current through the armature, and the current in 
passing from one commutator bar to the next is compelled 
to flow under all the poles on the dynamo. This is shown 
in Fig. 62. With a wave winding either two or four brushes 
may be used. This method of winding possesses the great 
advantage that the E. M. F. produced in each of the two 
paths in the armature must necessarily be equal, even ii 
the magnetic flux from the poles is very unequal. 

The diagram shows for convenience of representation 
a commutator «with onlly nine 'bars. 




Figure 62 
Wave winding on four pole dynamo. 



1'62 



The brushes in a four-pole dynamo are placed 90 degrees 
apart, in a six-pole dynamo 60 degrees apart on the com- 
mutator. In a four-pole dynamo brushes opposite each 
other should be connected together. In a six-pole dynamo 
three sets of brushes 120 degrees apart should be connected 
together to one pole or terminal of the dynamo. 

Another advantage of the wave winding as compared 
with the lap winding for small machines is that the number 
of turns of wire on the armature is half as great with the 
wave winding as with the lap winding. 

When one is calculating the voltage which will be pro- 
duced in a four-pole dynamo on which a wave winding is 
to be employed, it is necessary to have flux enough from 
each pole to produce only half the total voltage required. 



w — > 




Figure 63 
Lap winding on four pole dynamo 



163 



This is on account of the fact that there are only two 
paths for the armature current. 

The lap winding shown in Fig. 63 is perfectly analogous 
to the winding shown in Figs. 60 ana 61. In this machine 
there are four paths for the current through the windings 
of the armature, and the connections, instead of being com- 
plicated as with the wave winding, are as simple as with 
the Iwo-pole winding. By cro^s connecting opposite bars 
of the commutator it is possible to use either two or four 
brushes on a four-pole armature with a lap winding. In 
the wave winding the commutator bars are cross connected 
by the armature wires themselves. 

In the lap winding there are four paths for the arma- 
ture current through the armature. There must neces- 
sarily be four brushes on the commutator, unless the 
commutator is cross connected, and the voltage produced 
in each of the four circuits depends on the magnetic flux of 
its respective pair of poles. 

It may happen in this way, that after the armature has 
worn the bearings so as to be out of center in the fields 
that the E. M. F. in one circuit maj^ be considerably higher 
than that in the circuit on the opposite side of the arma- 
ture. • 

In a bi-polar machine the two sides of the coil must 
fpan nearly or quite 180 degrees of the armature in order 
that one side of each coil may be under a north pole while 
the other is under a south pole. In a four-pole machine 
each armature coil must span nearly or quite 90 degrees 
for the same reason. In a six-pole machine a *span in each 
coil of 60 degrees is required. 



164 



One peculiar thing is noticed in a wave windl^^ on a 
four-pole machine, when there are about half as man}' slots 
in the armature as there are bars in the commutator. One 
coil cannot be connected to the commutator and must be 
taped up and left in the armature without any electrica\ 
connection with the rest of the armature winding*. Tap- 
ing- up this coil makes the number of bars in the commu- 
tator one less than twice the number of slots in the arma- 
ture. Table Xo. 10 gives the armature windings and the size 
of the wire required for a number of the armatures most 
commonly used in the United States. 



165 



TABLE ]So. X, 



EDISON GENEEATOR WINDING. 







o 






1 








Kind 
of 


<t-l 

o 




<-< 


to 


O 


0) 


s3 _< 


Winding 




11 


S a; 

5§' 




1? 


43 

-3 


6a 




02 


■•^:^ 


Eh^ 


-^r. 


;z;jK 


?^ 


3 


Horizontal 


.072 


1 


3 


2 


44 


125 


6 




.050 


2 


2 


3 


58 


250 


12 


Vertical 


.148 


1 




3 


50 


125 


15 


it 


.180 


1 




2 


48 


125 


20 


(( 


.110 


4 




2 


40 


125 


20 


Horizontal 


.088 


6 




2 


66 


125 


25 


»i 


.162 


2 




1 


66 


125 


30 


•( 


.195 


2 




1 


58 


125 


45 


4( 


.083 


3 




2 


100 


500 


60 


Vertical 


.134 


2 




3 


58 


500 


100 


li 


.120 


4 




2 


80 


500 



^ 



•<1 



K 

D 

H 

O 
O 



H 



03 »H 

^ 5^ fl 

e ce p 

O o 



bCbCbb 
o O ^1 

^ -4-3 4J 



C be 

8.S 

CQfH 

5> 



08- 



bo- 

Si 



go 

QQ O 



o 
o 



u^dg snoo 



rt fl f= Pi 

Oj 0^ ^ c8 



'C "^ "TJ 'C Ti 'C "^ 
C G fl f3 C C fl 
53 c3 c3 cj 03 cj ^ 






00 oo 



9-1 1 Ai JO 9ZTS 



'■^OOi-t 2 
^ogSoO b<j t^ i^rH MC^005000-^0-«*QOjrt 



uoTioag 
JO snoo 
jaqranjsi: 



'*'^-*'<*'*o»«coint-03iococc»irtTHgsco?oo 

?OCOCO<©OCOOOSOOOt-OiOi0505»OOSCO»OCM 



Saip^TAi 
JO puix 






9JO0 

JO puix 






cc 



QQ 






-t-3 a> 



s^^ 

^'1 



OOh* 






c^^'*rL,a-SXOOTH'<H . .T-(OoH»«Oo 

e-iheh . .^^oo -g^^o;^ 03^^'Org 

[^ -4-3 -4^ 



OQOQ 



167 



TABLE No. X.-^Continued, 



WINDINGS OF ARC- ARMATURES. 



Armature 




o 


0-1 

.^1 


t-i 


umber 
urns per 
ayer 


11 




o^ 


«} 


J2;cfi 


Zi>^^ 


^Hh:i 


0?H 


Brush No. 7 


30 


.0?3 


8 


17 


36 


2000 


Brush No. 8 


65 


.083 


12 


21 


30 


2000 


Brush No. 9 


85 


.08:3 


24 


23 


19 


2000 


Brush No. 10 


100 


.083 


24 


Zi 


21 


2000 


Brush No 11 


125 


.083 


24 


22 


24 


2000 


T. H. Rine M. D. 
Schuyler 


50 


.072 


30 


15 


11 


2000 


50 


.057 


8 


8 


37 


1200 


Wood No. 8 


60 


.064 


120 


11 


6 


1200 


Wood No. 9 


80 


.072 


120 


13 


6 


1200 



J, 



168 



COMPOUNDING OF DYNAMOS. 

We have considered heretofore two general methods of 
field winding, viz: shunt and series. A combination of 
these two methods is called compound winding. In a shunt 
wound dynamo the excitation is almost constant, but the 
voltage produced by the dynamo decreases as the load in- 
creases, due to four causes: First, in order to obtain 
sparkless commutation the brushes are rocked forward into 
such a position that the coil, while short circuited by the 
brush, is under the influence of the pole toward which it is 
approaching. The armature reaction with the brushes in 
this position decreases the magnetic flux. This lowers the 
voltage. Second, the armature reaction tends to bunch the 
lines very greatly under one side of the pole 
and to thin them out under the other side 
of the pole. In a surface wound armature this action 
does not greatly alter the total magnetic flux, but when an 
ironcl'id armature is employed the armature teeth are satu- 
rated by the action of the normal fleld, and the effect of the 
armature reaction cannot greatly increase the flux of the 
lines under the dense end of the pole piece. Consequently 
all the lines which are prevented from passing into the ar- 
matiire at the other end of the pole piece practically dimin- 
ish the total magnetic flux by just this amount. Third, 
the current flowing through the shunt fields is decreased, 
owing to the loss of voltage produced ?n the armature by 
the effect of the armature reaction. Fourth, a rea- 
son which in large armatures is of practically^ little import- 
ance is the loss of voltage due to the resistance of the arma- 
ture. The combined efl:ect of these actions is to reduce the 
voltage from 5 to 25 per cent, between no load and full load. 



169 



It is desirable, of course, that the dynamo produce at the 
lamps a perfectly constant voltage. To satisfy this condi- 
tion the voltage at the dynamo at full load must be greater 
than the voltage at no load by the amount of the loss of 
voltage in the line. In order to accomplish this result and 
counteract the effect of armature reaction, a series winding 
is put on to the fields of the d^mamo. The effect of this 
series winding is to increase the ampere turns on the tield 
coils in proportion to the load. Therefore, when the arma- 
ture reaction tends to reduce the voltage by the greatest 
amount the series coils tend to increase the voltage to the 
greatest extent. By using the proper number of series 
turns the effect of armature reaction can be overcome and 
the voltage increased as the load increases, thus making up 




12 



x-x-x-x-x- 

Figure 64 
Diagram of compound winding in a dynamow 



170 



for line loss. Fig. 64 is the diagram of compound winding 
on a dynamo. Fig. 65 shows the effect of the series coil. 

Compound winding can be used on motors as well as 
dynamos. The effect here is to increase the torque and 
decrease the speed of the motor as the load increases. A 
little thought and a consideration of Fig. 20 will show that 
the torque or twisting effort is proportional to the current 



IZO 
to 





















^^'*'"^'*"«*».^^ 


n 




— ^ 







3 






^ 


-^^ 










N 










AMPERES 



Zoo 



BOO 



400 



Saa 



Figure 65 

Upper line shows the current and voltage when series coil is used. 

Lower line shows current and voltage when plain 

shunt winding is employed. 



which flows through an armature as long as the field is 
constant, and is always proportional to the product of the 
current through the armature and the strength of the field. 
An advantage of compound wound motors is that the speed 
variations which will occur when a plain series wound motor 
is used are confined within definite limits. At the same 
time the advantages of the series motor are obtained, viz: 
First, powerful starting torque; second, the decreased effect 



171 

of armature reaction, which shows itself in freedom from 
sparking at heavy loads. In calculating the number of am- 
pere turns required on a compound wound dynamo, it is 
necessary to calculate the number of ampere turns that 
would be required 'to force five or ten per cent, additional 
flux through the circuit. 

The effect of the shunt coils is usually sufficient in an 
ironclad armature to saturate to a considerable extent parts 
of the magnetic circuit. This makes it necessary that the 
ampere turns of the series coil should be much greater than 
would otherwise be necessary. 

In practice the ampere turns of a series coil at full load 
vary from one-third to one-half the ampere turns of the 
shunt coil. 



QUESTIONS OX CHAPTEK XIV. 



t. For what two purposes is wire used on a dynamo 
or motor? 

2. Why is it desirable to make the section of the field 
coil circular? 

3. What advantage is gained by placing the field coil 
near the air gap? 

4. In order to have a motor winding properly arranged, 
what must be the direction of the current in all the wires 
under each pole piece? 

5. Why does the coil winding on a four-pole dynamo 
span one-quarter of the circumference of the armature? 

6. How many degrees will a coil span in an armature 
intended for a ten-pole machine? Why? 

7.' Why is it necessary for the current in all the wires 
under the north pole of a motor to fiow in one direction and 
in the opposite direction under the adjacent pole? 

8- "What is the difference of potential between the first 
and last coils in fhe same layer of a two-pole, two-layer 
horizontally wound armature intended for 500 volts? 

9. If the armature has 64 sections, what would be the 
difference of potential between the third and fourth coils? 
Eleventh and twelfth? 



173 



10. In the same armature, what would be the differ- 
ence of potenftial between the upper and lower layers of 
wire? « 

11. What is a horizontally wound armature? 

12. What is a vertically wound armature? 

13. How is it possible to connect the armature to the 
commn'taitor so as to have the brushes set in any desired 
position? 

14. What is a wave winding? What is a lap winding? 

15. What are the advantages of wave winding for ma- 
chines up to 100 horse power? 

16. Why are the brushes in a six-pole dynamo placed 
60 degrees apart? 

17. Explain why a six-pole armature with a wave wind- 
ing may have its brusihes placed in the saime position as a 
bi-polar machine? 

18. A four-pole wave wound armature has a flux of 
one and a half millions of lines; the speed is 1,200 revolu- 
tions per minute; there are 45 slots in the armature and 
each coil has four turns in it. What will be the voltage 
produced? 

19. What will be the voltage produced bj the same 
armature if lap winding is used? 

20. What will be the relative resistance of the arma- 
tures with wave and lap windirg? 

21. How may a lap wound armature for a four-pole 
machine be connected so as to operate with two brushes? 



174 



22. What will be the difference in operation of a wave 
and a lap wound armature when the armature is not central 
in the pole pieces? 

23. Why is it impossible to use an armature in a four- 
pole wave "wound machine with an even number of slots if 
there are the same number of commutator bars as arma- 
ture slots? 

24. Make a diagram for a wave winding- for a four-pole 
armature having 12 slots in the armature and 23 bars in the 
commutator? 

25. 'What is a compound wound dynamo? 

26. What is the object of putting a series coil on a 
dynamo? 

27. Wliy does the voltage of a plain siiunt wound 
dynamo decrease with the load? 

28. If a bi-polar dynamo produces 200 amperes and 
the shunt ampere turns are 2,600 on each coil and there are 
eight turns in the series coil, what will be the total ampere 
turns on each field coil at full load? 

29. What is the effect of compound winding on motors? 

30. What are the advantages of compound wound mo- 
tors over plain s-hunt wound motors? 

31. Why will a 500-volt compound wound dynamo that 
operates very well on 500 volts greatly over-compound whea 
operated at 250 volts? 



CHAPTER XV. 



PROPER METHODS OF CONNECTING UP DYNAMOS 

AND MOTORS. 



It is a factj and one which for a long time remained 
undiscovered, that a dynamo will excite itself when run at 
the proper speed and with proper connections between ar- 
mature and fields. It is also true that in order that a ma- 
chine may excite itself or excite its own field magnets, it is 
first necessary to send a current from an external source 
around the field magnets. This current drives a certain 
amount of flux through the magnetic circuit, and since most 
of the magnetic circuit is composed of iron, a part of this 
^ux does not disappear when the current is cut off. This 
permanent magnetism is called residual magnetism. The 
residual magnetism will be greater in a dynamo with an 
ironclad armature than in one with a smooth core, because 
the magnetic circuit is so much more perfect. The residual 
magnetism in most cases will be greater with cast iron field 
cores than with wrought iron or soft steel. ' The amount 
of this residual magnetism with an ironclad armature varies 
from one to five per cent, of the total fiux with fully excited 
fields. The writer has seen a 500-volt street railway gen- 
erator w^hich had a residual magnetism such that it pro- 
duced 25 volts when the armature was run at full speed. 
This residual magnetism produces a voltage in a certain 
direction depending upon the way in which the current has 



176 



been flowing through the field coils and upon the way in 
which the armature is connected up to the commutator. In 
order that a d3^namo may excite itself, it is necessary that 
the current produced by the residual magnetism shall flow 
in such a direction as to sitrengthen this re- 
sidual magnetism. If the eurremt produced by the 
residual magnetism flows through the field coils in the oppo- 
site direction this wull tend to weaken the residual mag- 
netism and consequently to reduce the current which flows. 
If, on the other hand, the current produced b}^ the residual 
magnetism flow^s through the fleld coils in such a direction 
as to strengthen it, the greater magnetism which results 
will strengthen the current, and this in turn strengthens 
the field, and this process goes on until further increase in 
the magnetism is prevented by the saturation of some part 
of the magnetic aircuit. It often -happens that 
when an armature is re-wound tihe conneotions 
between the winding and the commutator are made in such a 
way as to reverse the direction in which current fiows from 
the armature; that is, the brush which before the armature 
was re-w^ound w^as a positive brush may become a negative 
brush. This reversal of the direction in which current 
flows in connecting up an armature is easily made and very 
frequently occurs. The re-wound armature when put into 
the old field 'produces a current which tends to flow in the 
opposite direction from that of the old armature. 

This current tends to reduce instead of strengthen the 
residual magnetism, and the result is that the machine will 
not excite itself or refuses to build up. In order to correct 
this difficulty, it is only necessary to reverse the connections 
between the armature and the field coil, so that the current 
produced by the residual magnetism may flow in suoh a 



177 

direction as to strengthen this residual magnetism. To do 
this either the leads from the armature may be crossed or 
the leads from the field may be reversed. When the fields 
have both series and shunt coils it is usually more conven- 
ient to reverse the armature leads than it is to reverse the 
leads from both series and shunt coils. When, however, 
the field has only a single winding it will usually be found 
to be more convenient to reverse the field leads. An excel- 
lent method of determining whether the armature and fields 
are connected in such a way that the machine will not build 
up is to measure the residual magnetism with a volt meter 
with the field circuit open, then close the field circuit, and 
if the voltage drops it is almost a certain indication that 
the armature and field connections are reversed. In con- 
necting up a compound wound dynamo to its circuit it is 
necessary to be sure that the shunt coils and series coils 
tend to drive the lines around the magnetic circuit in the 
same direction. If the series coil is connected up in the 
opposite direction to -the shunt coil the dynamo will build 
up all right and will work satisfactorily on very light loads. 
When, however, the load becomes even, five or ten per cent, 
of full load, the voltage drops off very rapidly and it is im- 
possible to get full voltage with even half the load on. This 
is because the ampere turns due to the series coil decrease 
the total ampere turns acting on the magnetic circuit in- 
stead of increasing them as the load comes on. This lowers 
the magnetic flux and of course lowers the resulting volt- 
age. 

All shunt and compound wound dynamos are provided 
with a rheostat, which is placed in series with the shunt field 
magnetizing circuit. This rheostat is a resistance capable 
of adjustment by hand by means of which the current flow- 



178 

ing" throug'h the shunt first coils may be regulated. Wlien 
this resistance is all cut out tne maximum current flows 
through the shunt fields and they consequenftly have a max- 
imum magnetizing- power and the maximum voltage is pro- 
duced. If this voltage is too high, it is necessary only to 
insert more resistance in the shunt fields by a movement of 
the rheostat and thus cut down the magnetizing power of 
the fields and therefore the voltage produced by the dy- 
mamo. 

It sometimes (happens that a dynamo refuses to build 
up because there is 'so much resistance in the rheostat that 
the current produced 'by the residual magnetism is not 
powerful enough to sufficiently increase the magnetism of 
the fields to begin 'the building up process. Therefore if a 
machine refuses persistently to build up it is a good plan 
to short circuit the rheostat. This cuts out the resistance 
and at the same time bridges any possible open circuit that 
there may be in the rheostat. The rheostat should be ar- 
ranged 90 that the field circuit can never oe suddenly brok- 
en. This is to avoid the possibility of breaking down the 
insulation of the field coils by the so-called field discharge. 
A field discharge is said to occur when the shunt circuit of 
a dynamo in operaftion is suddenly opened. Anyone who has 
done this knows that a yery lomg thin arc is produced; the 
length of the arc indicates the high voltage produced by 
the discharge and the small size of the arc shows that the 
current is comparatively weak. A calculation will show 
w^hat the voltage produced by such a field discharge may be. 
Suppose a shunt field of a 110-volt dynamo is composed of 
two coils each of 1,500 turns, also that the magnetic flux 
passing thrugh these coils amounts to 4,500,000 lines. Tf 
this circuit is opened in one second, the voltage which would 
be produced will be 2x1,500x4,500,000 divided by 100,000,000 



179 



(>r 135 vcfltts. When the field dircuit is opened in 1-100 of a 
.second, tihe voltage will be 

1,500x2x4,500,000 



100,000,000 l,500x'2x4,500,0O0x!l0O 

equals 

1 100,000,000 

100 

or 13,500 volts. Such a voltage as this is very apt to punc- 
ture the insulation of a field coil and care should be taken 
that the circuit is never opened in such a way as to expose 
the insulation to such a strain. The production of an ex- 
tremely high voltage in this manner is simply a reproduc- 
tion on a larger scale of the ordinary battery and spark 
coil used for igniting gas engines. In the ordinary spark 
coil the current from a battery of two or three volts is 
passed around a magnet and then suddenly opened with 
the production of a spark from one-fourth to one inch in 
length. Here we have the production of many hundreds of 
volts from two or three. The same multiplication takes 
place when a shunt field is opened suddenly. 

Rheostats for the shunt circuit of a dynamo should have 
sufficient resistance, so that when it is all inserted the volt- 
age in the dynamo will slowly sink to zero. This method 
of stopping the action of a dynamo is perfectly safe and 
should be followed wherever possible. Fig. 66 shows an- 
other diagram of the connections of a compound wound 
dynamo. 

Almost all stationary motors are plain shunt wound 
machines. Fig. 67 is a diagram of the way in which these 



180 



motors should be connected up. The essential point in 
this scheme is that the shuht field circuit be always closed 
through the rheostat and armature so that a field discharge 
is impossible. The rheostat is inserted for the purpose of 
not permitting too great a rush of current through the 
armature before it has attained its speed and consequently 
its counter E. M. F. 




Figure 66 
Biagram of connections of compound wound dynamo 



It this rheostat were arranged so that when it wds 
thrown off, the armaiture circuit should be lopened, the open- 
ing of the main switch would break the current through the 
shunt fields and produce a field discharge. An arrangement of 
a starting rheostat like this has been )the cause of numberl^ 
burn-outs in field coils. If, however, the resistance of the 
starting rheostat is simply sufficient to choke the current 



181 



back to the desired amount and does never open tlie arma- 
ture circuit, the opening" of the main switch simply cuts 
the current oif the motor. The instant after the main 
switch is opened the motor armature becomes a dynamo 
armature at practically the same voltage and supplies the 
field trolls with current almost as long as the armature 
continues to revolve. In this way there is absolutely no 
possibility of such a disturbance of the shunt circuit such as 
will produce any abnormal strain on the insulaltioa. 




Figure 67 
Diagram of connections of plain shunt wound motoTo 



An automatic rheostat or starting box is one which is 
provided with a spring, which tends to throw the handle 
back to the position of greatest resistance. (See Fig. 68.) 
A magnet holds the handle in opposition to the spring in 
that position in which all the resistance is cut out^ The 



IB2 



mag-net is usually energized by the current which passes 
through the shunt coils on the motor. If, for any reason, 
the power which op'erates the motor should fail, the mag- 
net will weaken and rele-ase its hold. The spring will foice 
the handle back to the position of greatest resistance, and 
when the power is again thrown on the line the motor wili 
start up in the ordinary way. 




Figure 68 
Blagvam of automatic starting box showing coniiGetSo53S 



If the resistance in the starting rheostat were entirely 
cut out and the power was thrown onto the motor from 
ten to a hundred times full load current would flow through 
the armature, causing very bad sparking and almost cer- 
tainly blowing the fuses which protect the motor. 

Overload rheostats are those in which the resistance is 
cut in where the current exceeds a certain ajciount. 



183 

In one design of overload rheostat the mag-net spok- 
en of above has two windings, a shunt winding which is 
the more powerful and a series winding in oppositon to it. 
With normal load the series winding does not diminish the 
strength of the magnet sufficiently to release the rheostat 
handle, but with an overload the magnet is weakened suffi- 
ciently so as to release tli'e rheostat handle and insert the 
resistance of the starting rheostat in t-he armature circuit 



A 



QUESTIONS OX CHAPTER XV. 



1. What is the effect of residual magnetism in the self- 
excitation of dynamos? 

2. Would a dynamo in which there was no residual 
magnetism excite itself? 

3. Why will reversing the connections of the shunt coil 
prevent a dynamo from generating? 

4. What is the amount of residual magnetism in or 
"Jinary iron-clad dynamos? 

5. When a machine begins to build up, vsKhat causes 
the voltage to stop rising? 

6. Tf a dynamo could be made without iron that would 
build up if supplied with a residual field from an external 
source, what ^vould be true of the voltage generated by 
such a dynamo? 

7. If an armature fails to build up, wha-t course should 
be pursued? 

8. How is it possible to be certain that the armature 
and field magnet connections are properly made with refer- 
ence to the residual magne-tism? 

9. How w;ill a compound wound dynamo act when the 
series and shunt coils are reversed? 

10. W%y does moving the arm of a rheostat' raise or 
lower the voltage cf a shunt or compound wound dynamo? 

11. What is a field discharge? 



185 

12. What will be the voltage Irom a field discharge 
from the Edison dynamo on Fig. 26, df there are 1,500 turns 
on each coil and the circuit is broken in 1-50 of a se<iond? 

13. What will be tne voltage produced if there aro, 
6,000 turns on each coil and the circuit is broken in 1-80 of 
a second? 

14. How should the rheostat in series with the shunt 
coils of a dynamo be arranged? 

15. Why is it desirable to have* a starting box for a 
shunt wound motor that will never break the circuit? 

16. Explain why a field discharge is impossible witih a 
starting box arranged in this way. 

17. What is the object of the automatic starting box? 

18. How are overload automatic rheostats arranged? 



13 



y^ 



CHAPTER XVT. 

DISEASES OF DYNAMOS AND MOTORS: THEIR SYMP- 
TOMS AND HOW TO CURE THEM. 



A. — Open Circmts. 

The currenrt. in an armature flows from section to sec- 
tion of the armature winding- and usually has to pass to 
the commutator to pass from one seotion to the next. Oc- 
casionally one of the lead wires from the armature wind- 
ing to the commutiajtor becom'es broken; this prevents the 
armature current form flowing through this path in the 
armature. But it will be noticed that when the coil con- 
taining the broken wire is short circuited by the brush, 
current will flof\v througlh the ^vhole armature in a normal 
maoiner. As soon, however, as this coil leaves the brush 
the armature current in attempting to complete its circuit 
through this half of the armature winding will arc from 
one commutator bar to the next one in its attempt to flow 
through the circuit in spite of the broken w^ire. This arc 
wdll show itself as a very bad spark at light loads or as a 
ring of fire traveling around the commutator if the voltage 
is high enough to keep up the arc. With heavy loads the 
sparking becomes very furions and the insulation which 
separates the two commutator bars between which the arc 
occurs will be melted out. Any one who has once seen the 
effect of an open circuit on a commutator cannot fail to 
recognize it if seen a second time. It may be that the 
open circuit is caused by the melting of the solder, which 



187 

attaches tihe armature wire to* the cO'mmxitart:or bar. If tihe 
armature winding* is coimpleted by hajving- the outslide of 
one coil and the inside of the next coil soldered into the 
coonmutator bar the melting* of the siolder will make a true 
open circuit. If, however, the connection between the ar- 
ma/ture winding and the commutator bar is such as is 
shown in Fig-s. 57, 58 and 59, the open circuit will be only 
partial and will show itself only in increased sparking*. 

The cure for an open circuit is obviou'sly to find the 
broken wire and repair it. If the trouble has been due to 
the melting" of the solder in the commutator bars these 
wires shooild be thorooighly re-soldered ait once. If, how- 
ever, the wire is broken in the armature somewhere and it 
is desired to operate the machine temporarily, the two bars 
across which the arc. occurs may be soldered tog*ether or 
connected together in some other way, so that the arma- 
ture current may be able to complete Its circuit through 
this temporary bridg*e. It is possible to run an armature 
temporarily repaired in this way for several weeks with- 
out se>rious trouble. 

B. — Short Circoiits. 

If, in a properly wound and connected armature, two 
of the commutator bars be connected together, the voltage 
which is produced in the coil connecting these bars will 
produce -a very great local current, which will flow through 
the coil and complete its circuit acress the two commutator 
bars. Such a co>nnection would be a short circuit, and any 
connection that allows a local current to flow through a 
part of the armature winding is called a short circuit. 

Suppose an armature with a resistance of 1-10 of an 
ohpa has fifty coils; the resistance oi each path in the ar- 



188 

mature will be 1-5 of an ohm and the resistance of each 
coil Avill be 1-25 of 1-5, or 1-125 of an ohm. If, now, this 
armature is capable of producing 250 volts each coil in it 
generates 10 volts on the average. When the armature is 
working properiy this 10 volts simply adds itself to the 
voltage produced by the other coils »a.nd is expended in 
forcing the armature current thro'ugh the external resist- 
ance. If, however, the t^vo bars to which thi-s coil is con- 
nected be short circuited, this 10 volts will expend itself in 
producing a \ery great local current through this short 
circuited coil. The coil generates 10 volts and its resist- 
ance is 1-125 of an ohm. The current which will flow then 
will be 1,250 amperes; this is enough to heat the eoil red 
hot and entirely destroy the insulation in its neighbor- 
hood. Trouble of this sort is the most destructive that can 
occur in an armature, for it usually cbmpels the re-winding 
of the whole armature. If the short circuit is discovered 
before the coil has been sufhciently heated to destroy the 
insailation, and it is absolutely necessary to use the arma- 
tnre temporarily and the point at which the coil is short 
circuited cannot be discovered, -each turn of the short cir- 
cuited coil may be cut in two and then the two commuta- 
tor bars between which this coil is connected may be sold- 
ered together. It often happens that one wire in a coil 
touches its neighbor at some point, and when this occurs 
only one turn of the coil will be short circuited and only 
one turn will get hot. 

A shorrb circuited coil always shows itself by getting 
warmer than its neighbors at first, and if not soooi discov- 
ered will smoke and finally set fire to the insnlation. 

If an armature is completely short circuited, as, for 
instance, from top to bottom layers in a horizontally wound 
armature or fro.m coil to coil in a vertically wound arma- 



189 

tuTe, it will refuse to build up if it is a g-eneraitor and will 
turn >a half revolution at a time if it is a two-pole motor, 
or a quarter revolution if it is a four-pole motor. In a bi- 
polar machine the short circuit of the armature will not 
affect the distribution of the current when the short cir- 
cuit is 90 degrees fromi the brushes, for then the two oppo- 
site, sides of the commutator are at no difference of poten- 
tial and no current \Aall flow in the short circuit. 

C. — Sparking. 

The principles which govern perfect commutation were 
explained in the chapter on "Sparking," but many other 
causes beside imx^roper design of the dynamo may cause a 
machine to spark. When the commuta»tor is in good con- 
dition, trueand smooth, and the brushes have a firm con- 
tact against it and the m'achine invariably sparks at a 
heavy load, the trouble may be attributed to a poor design. 
In a well designed machine 'the causes for sparking will be 
a rough commutator, a commutator out of round, or 
brushes not having sufficient contact against the commu- 
tator. 

In fact, the causes of sparking may be divided into two 
classes — sparking from electrical causes and sparking from 
mechanical causes. The cause of the electrical sparking 
was explained in Chapter XV. 

In most machines built at the present time any spark- 
ing that there may be is principally due to mechanical 
causes. It is clear that in order to have sparkless running 
the brushes must at all times touch the commutator. The 
fact that from some cause or other the brushes do not touch 
the commutator all the time is the cause of most cases of 
sparking. If the brush is not free to move, sparking will 



190 

result, for even in the best machines there will be some 
movement of the commutator with reference to the brush, 
and if the brush cannot follow it there will be a very short 
arc that maybe will n'ot be seen unrbil the oommuta'tor is 
blackened and burned at one spot. 

When an armature is slightly out of balance and is Tun- 
ing at a very high speed, there will be a vibration of the 
commutator, and if the machine is to run sparkless the 
brushes will have to follow this vibration of the commu- 
tator. In order that the brushes may follow the movements 
of a commutator that is not running perfectly true, the mov- 
ing part of the brushholder should be as light as possible and 
the spring tension that holds the brush against the commu- 
tator should be as heavy as possible. This condition is best 
fulfilled in a brushholder in which the brush alone moves, 
for in such a brushholder the inertia of the moving part is 
as small as it is possible to obtain, and consequently a com- 
paratively small pressure will enable such a brush to follow 
the uneven motions of the surface of the commutator. 

The writer once saw a motor which ran at 3,700 revolu- 
tions per minute, which could not be prevented from spark- 
ing when solid brushes were used, owing to the fact that 
the commutator did not run perfectly true. When leaf cop- 
per brushes were employed on this same commutator the 
motor ran almost sparkless, due to the fact that the copper, 
with its large number of separate leaves, always made con- 
tact with the commutator. Another cause which prevents 
the brush from touching the metallic part of the commuta- 
tor is the use of insulation between the commutator bars 
that does not wear down as fast as the commutator bars 
themselves. After the machine has run for a time these 



191 

insulations project above the copper bars and produce both 
heating- and sparking. Poor construction of the commu- 
tator is another prolific cause of sparking. If the commu- 
tator is not perfectly tight the centrifugal force will throw 
out one bar more than its neighbor, and consequently there 
will be spots on the commutator that the brush cannot 
make contact with. A commutator must be mechanically 
clean in order to run sparklessly. Spots of paint or dirt 
may be on a coimmutator and get between the brush and 
the copper bar, and so prevent perfect contact at one point 
in the commutator and produce sparking. 

A cause which produces as much sparking as improper 
mechanical arrangement of the brushholder is improper set- 
ting of the brushes. As explained in the chapter on spark- 
ing, there is a proper place for the brushes, and if they are 
not placed in this position there will be a tendency to spark. 
The brushes being in a wrong position will first heat the 
commutator and roughen it, and when the surface of the 
commutator is impaired, sparking will result. In a dynamo 
the brushes should be rocked forward in the direction of 
rotation into such a position at no load that the voltage is 
two or three per cent, lower than the maximum voltage. 
In a motor the brushes should be rocked backward into such 
a position thai at no load the speed is increased about two 
per cent, above tfhe lowest speed. 

1). — ^H'eating the Commutaitor. 

Abnormal heating of th^ commutator is due tO One of 
four causes: First, friction of the brush against the com- 
mutator; second, improper position of the brushes SO that 
there is forced commutation; third, abnormally heavy €ur« 
rents being taken from the armature; fourth, poor contact 



192 

between brushes and commutator. As soon as it is deter- 
mined to widch of t'heise four causes the heating- is due, the 
remedy in each case is obvious. The heating of the com- 
mu'tator in many iTistamces may be remedied by the substi- 
tution of copper brushes for carbon brushes. First, because 
the friction between the commutator and the coppe-r brush 
need not be so great as between the commutator and the 
carbon brush, and still more important because the electri- 
cal resistance between the co-mmutator and the brush is 
yery much less with the copper than with the carbon,* The 
objection to the use of the copper brush on any commuta- 
tor is that unless it is given very careful attention it will 
cut the comjmiutator in the same way and for the same 
reason that a bearing without oil will cut. 
E. — Grooinds, 

When a machine is out of order the first thing to do in 
testing it is to find whether or no there is a connection be- 
tween the "winding and the frame of the dynamo or motor. 
Such a connection is called a ground. A single ground on 
a machine does not of itself impair its action; ix only ren- 
ders the insulation in some other part of the machine very 
liable to break down. When there are two grounds on a 
machine there will be a short circuit of more or less of the 
winding, for the current will run from one part of the 
T\*inding through one ground through the frame oi the 
machine through the second ground to the other part of 
the winding. Such a short circuit usually shofws itself 
very plainly by burning the insulation and usually stop- 
ping the operation of the machine. 

Some motors, as, for instance, street car motors, are 
built with one end of the winding grounded to the frame. 
The object of this is to allow the current after it has pass- 



193 

ed througli the motor and done its work to escape tlhrongh 
the motor frame, axles and wheels of the car to the rails. 
When guch a motor as this is to be tested for a ground it 
is necessary to open the connection between the winding- 
and field frame before the test is made. Testing for ground 
is usually done with a small dynamo provided with a field 
made of permanent magnets and operated by hand. When 
current passes through the circuit its presfence is made 
known by the ringing oi a pair of smiali bells. 

Partial grounds, as, for instance, in the mica insulation 
of a commutator, may cause isevere heating of a part of the 
commutator, due to the arc that is formed between the 
commutator bars and the commutator core. It is possible 
by the use of a- Wegton volt m-eter to determine just where 
the ground is in an armature, provided the ground is per- 
fect or nearly so. Pass current from an external source 
between the armature core and the winding, and tesft the 
voltage when the wire <rarrying tlie current rests upon a 
certain commutator bar. Next, move the wire carrying the 
current four or -Q-ve bars in one direction, and measure 
the voltage again. If the voltage is higher in the second 
case tlhan in the first, it is clear that the current passes 
through more of tOie armature winding in the second case 
than in the first. It will be necessary then to move the 
other way. Keep on testing in this manner until a bar is 
found that gives the lowest valtage. Either the ground is 
in this co'mmutator bar o<r it is in the armature winding in 
the coil that is connected to this bar. To determine this 
point, unsolder the larmature wire from the commutator 
bar and test each separately. Even when the ground is 
imperfect it is p'" .sible to locate it within one or two bars 
of its exaot poslton. The armature wires may be unsold- 



194 

ered from several coimmutator bars and each coil tes-ted 
separiately with a maig-neto bell. 

A single ground between a series and a shunt coil may 
practically short circuit a dynamo, for the series and 
shunt coils are connected tog*e-ther on oaie side of the naa- 
chine, and if a ground should occur betweem the other ex- 
tremity of the shunt coil and a series coil, a complete short 
circuit would result, 
F. — Open Circuit in Field Coil. 

If for some reaison one of the wires in the shunt field 
codl of a motoror dynamo should become broken, the ma- 
chine would not operate, because it would be impossible to 
produce any magnetic flux. This would show itself in a 
dynamo by the refusal of the machine to build up. In a 
motor it would show itself by the refusal of the motor to 
pull any load and by blo^\dng' the fuses when the starting 
rheo'stat is nearly cut out. In a motor a very easy way 
to test this is tO' see whether the fields are excited as soon 
as the s"\vitch is clo'sed by presenting a knife or any mag- 
netic object to the magnet pole. Another way of making 
the test is to open the armature circuit and clo'se the 
main s^\dtc!h, and then open it slowly. If the field wdre is 
broken there will be no current; if the field is in perfect 
conditon there will be an arc upon the opening" of the 
switch. If there are two or more field coils on the motor 
it is easy to determine the one in which the broken wire is 
situated by turning on the current and then short circuit- 
ing one after the other until one is found which, when 
short circuited, allows the current to flow through the 
other coils. This coil will have to be removed and rewound. 

G.— Short Circuit in Field Coils. 

If, for any reason, the beginning atnd 'end of a eoil come 
in contact, the resistance of the coil between these two 



195 

points is cut out, and the current will flow only through a 
part of the coil. In practice this coiil will show itself by run- 
ning* cooler than the others, because the same current runs 
through a greater resistance through the other coils than in 
the short circuited ooil. By measuring the voltage across 
the damaged coil and across a good coil th^r amount of the 
damaged coil which is short circuited may be determined. 
This coil will have to be removed and rewound. If, from 
any cause, such as long use or improper ventilation, the 
insulation on the wire in a coil becomes charred, so that it 
is no longer a good insulator, the current, instead of flowing 
through all the turns of a coil, will leak from layer to layer. 
Such a coil is said to Odc "burned out," and mav be detected 
by running cooler than a coil in good condition and by 
having very much less magnetizing power. It is to be 
observed that when a shunt field coil becomes short cir- 
cuited or "burned out," it throv/s a great deal more load 
on the other field coils; for instance, if there are two field 
coils on a motor which normally take one ampere at 220 
volts, the watts wasted in each coil will be 110. If, now, 
one of these coils be short circuited, the only resistance in 
the circuit will be that of the otner coil, and the current 
through this coil will be two amperes, because one coil has 
only half the resistance of two. The voltage on this coil 
will be 220 volts; therefore 440 watts will be wasted in it, or 
four times the normal heat loss. It is easy to see that if 
one coil should become short circuited this would be almost 
certain to burn out the other coil. 

H. — Improper Connection of Field Coils. 

It is easy to see that in order to be effective the field 
coil must be connected up in such a way that it forces the 
flux around the circuit in the same direction 



196 

that its mates do. Thus in the Edison dynamo 
shown in Fig. 23, if the 'field coil should be 
connected up in such a direction as to make both pole 
pieces north poles, it is obvious that there would be no 
raag-netic flux through the armature. If this machine were 
used as a motor the armature would not run with even a 
small load. In order to detect this trouble it is necessary 
lo test the polarity, of the field coils with a compass. If it 
is found that both poles are the same it will be necessary 
to reverse the connections of one of the field coils. If the 
field coils should be connected up in this way on a dynamo 
it would refuse to build up, and the only way to detect the 
trouble would be to send current through the field coils 
from an external source and test the polarity of the pole 
pieces with a compass. Great care should be taken when 
putting on a repaired field coil to see that it is connected up 
correctly. 
L— Heating of Field Coils. 

When all the field coils on a new machine rise to a tem- 
perature of over 70 degrees Fahrenheit above the surround- 
ing air they are too warm to be chirable, and it is an indi- 
cation that not enoug^i w^ire has been used in the field coil 
by the manufacturer. 

When on an old machine a coil gets warm while an- 
other is much cooler, it is, as explained above, usually due 
to a short circuit or a partial bum out in the cool coil. 
The coil that is hot is the one that is still ini good condi- 
tion. The only way to prevent the heating in all the shunt 
field coils is to increase the amount of wire on the coils. 
J. — Noise When a Machine is in Operation. 

In machines having ironclad armature a humaning or 
singing noise is ocoasionally heard when the armataires run 



197 

with fully excited fields. This occurs in machines which 
have short air gaps usually, and is due to the magneftic pull 
exerted on the tooth of the armature as it suddenly comes 
under the influence of the field magnet. The mechanical 
force due to the magnetic attractino between the armature 
and field magnet is sufficient to mechanically stretch out 
the tooth a fraction of a thousandth part of an inch. This 
produces a small air wave and a rapid successiooi of these 
as the armature passes under the field magnet produces 
the noise. 

In itself the noise is not harmful but is occasionally 
an indication of tufting ot the magnetic lines as ti^ey pass 
from the pole piece into the armature teeth. As was 
learned in a former chapter, this tufting of the magnetic 
lines produces edd}' currents in a solid pole piece which 
wastef ully heats itr- 



QUESTIONS ON CHAPTER XVh 

1. What is an open circuit? 

2. How does an open circuit show itself? 

3. How may an open circuit be tempcNrarily repaired? 

4. What is a short circuit? 

5. How much current wall flow in a short circuited 
coil in a 110-volt armature, if there are 40 sections in the 
commutator and the resistance of the armature is 2-100 oi 
an ohm? 

6. How will a short circuit show itself? 

7. What will be the effect of a short circuit between 
the upper and lower halves of a horizontally wound arma- 
ture? 

8. How will a short circuited armature operate dn a 
motor? 

9o T\%at is the most ordinary cause of sparking? 

10. What is the principal mechanical necessity in or- 
djer to prevent sparking? 

11. Name some of the causes which prevent the brushes 
from touching the commutator continually? 

12. What is the objection to a heavy brush holder v^th 
a carbon brush rigidly clamped into it? 

13. What is the effect of improper setting cf the 
brushes? 



199 



14. In what direction should dynamo brushes be rock- 
ed as the load increases to prevent sparking? 

15. In what direction should motor brusihes be rocked? 

16. What are cfour causes of heating- the commutator 
of a machine? 

17. What is a ground? 

18. Whait is the effect lof two grounds on 'the tsiame 
m,achine? 

19. Is it possible to successfully operate a grounded 
machine? 

20. WTiat is necessary to do before a street car motor 
can be tested for a ground? 

21. How is it possible with a Weston volt meter to 
locate the position of a ground on an armature? 

22. How may a ground between a series and a shunt 
coil short circuit a machine? 

23. How will an open circuited field coil show itself? 

24. How is it possible to locate an open circuited field 
Ln a motor? 

25. What is the effect of a short circuit in a field coil? 

26. Why will a short circuited field coil run cool while 
a short circuited armature coil becomes very warm? 

27. Why will one short circuited field coil almost cer- 
tainly burn out its mate if there are only two on the ma^ 
chine? 



200 

28. \^%at is the effect of improper connection of the 
field coils? 

29. 'When all the field coils on a dynaimo or motor run 
warm (how can they be made to run cooler? 

30. What is the cause of the humming noise sometimes 
heard in machines ^th iron-clad armatures? 



CHAPTER XVII. 



ARC AND IXCAXDESCBXT LAMPS. 



A large part of the electric power which is produced at 
the present time is used for electric lighting. To produce 
this light two devices are used; one is called the incandes- 
cent lamp, the other the arc lamp. In the incandescent lamp 
a comparatively small amount of current is forced through 
a thin carbon wire of very high resistance. This carbon 
wire is enclosed in a glass bulb which is completely ex- 
hausted of air and is supposed to contain nearly a perfect 
vacuum. 

The object of extracting the air is two-fold: First, if 
any ox,v gen (were left inside the bulb, the carbon when at a 
high temperature would greedily combine with all the oxy- 
gen in the globe, or the filament would burn up. Another 
reason w^hj^ a vacuum is desirable is that if there were 
gases inside the bulb the heat of the filament would be more 
readily dissipated, because the particles of gas would be 
heated verj'' much by contact with the incandescent carbon 
filament and then pass to the glasis walls of the bulb, and 
give up their heat to it, and then return to the filament 
to be re-heated. In other words, if there were gases in the 
bulb, the incandescent filament would lose its heat througli 
both radiation and conductioTi. When all the gases are 
exhausted from the bulb the only loss is the loss by radia- 
tion, 

14 



The current is brouglhu to the carbon fil- 
ament by two platinum wires which are melted 
into the glaas. It is necessary to use platinum wire 
for this purpose, for the reason that platinum and glass ex- 
pand with rise of temperature at about equal rates; all oth- 
er metals expand about twice as rapidly as glass does, and^ 
contract twice as fast, so that if iron wires were fused into 
the glass at a high temperature, a small space would he 
left between the wire and the glass when the wire was cold^ 
through which the air could slowly creep and spoil th^ 
vacuum. 

The light given off by an incandescent lamp increases 
very rapidly with the temperature. A lamp on 100 volts is 
nearly as hot as when at 110 volts, but only gives about 
half the light. 

It is desirable to work the lamps at as high a tempera- 
ture as possible, in order to get as much light as possible 
out of them, but the higher the temperature or voltage at 
which they are worked the sooner they burn out. 

A lamp may give a very good light at 110 volts and last 
for 600 hours that would not last 100 hours on 112 or 113 
volts. A very necessary condition to the long life of an 
incandescent larpp worked at a very high temperature is 
that the voltage be constant. 

Therefore, for the successful operation of high efficiency 
lamps, or those in which the carbon filament is very hot, a 
very steady and unvarying voltage is essential. The most 
common incandescent lamp produces about 16 candle power, 
is operated at 110 volts and requires from 2% to 4 watts per 
candle or from 40 to 64 watts for the lamp. As an average, 
it may be said that each lamp takes Yz ampere at 110 volts, 



203 

oi» M watts; that is, about 3l^ watts per candle. As the in- 
candescent lamp gets old the light that it produces gets 
weaker until it becomes so poor a device for transforming 
electric energy into light that it pays to take the lamp down 
and substitute a new one. 

It is likely that some time the heat in the filament of 
an incandescent lamp will be used as the heat from the gas 
is in a Welsbach gas burner, to heat an oxide that has the 
faculty of giving off a great deal more light at a low tem- 
perature than carbon has. If this could be successfully 
done it would very greatly increase the light produced by 
the incandescent lamp. 

The arc lamp is best adapted for lighting streets or 
large areas in an interior. In the arc lamp a small part of 
a pencil of carbon is heated intensely by the passage 
of a considerable current from one pencil to another across 
an air space. The carbon is heated to about 7000 degrees 
F. until it probably vaporizes, and this very high tempera- 
ture produces the most intense light that is known. 

The ordinary incandescent lamp requires 3^2 watts per 
candle power. 

A current of 10 amperes at 45 watts produces 2000 can- 
dle power in an arc lamp, or about 41/3 candle power per 
watt. 

The objection to the arc light is that it is so intense that 
it casts deep shadows and dazzles the eye. This difficulty 
has been partly overcome in the enclosed arc lamps that are 
coming into such general use. 

In these lamps the arc is produced in a glass globe that 
i& arranged so that very little fresh air can get in. 



204 



The oxygen in the globe is very soon consumed by the 
carbon and the carbon thus burns away much more slowly 
than it woiild in the open air. 

The arc lamp must be provided with automatic mechan- 
ism that will feed the carbon down as fast as it is consumed 
and so keep the arc the same length. The mechanism for 
accomplishing this result in the old lamps was in some 
cases quite complicated, but in the modern lamp there is 
very little mechanism. 

In general, the operating mechanism of an arc lamp is 
composed of a magnet that grows weaker as the arc gets 
larger, and at a certain point grows weak enough to release 
a clutch that allows the carbons to come closer together. 




Figure 69 
Diagram showing action of series arc lamp^ 



305 



Before the carbons can drop together the current through 
the lamp is changed and the magnet strengthened and the 
motion of the carbons arrested, and they are drawn a prop- 
er distance apart. 

Figs. 69 and 70 are daagranas tha/t illustrate the action 
of the series lamp and the modern constant potential lamp. 

In the series lamp, in which the strength of the current 
is constant, the strength of the magnet is varied by using 
a series coil and a shunt Kioil an opposiition to it. The shunt 
coil is connected across the arc and when the arc is long 
the current in this coil is greait and the 'strength of the com- 
bined series and shunt coils is small, thus allowing the car- 
bons to drop together. 




Figure 70 
Diagram showing action of constant potential arc lamp. 



QUESTIONS ON CHAPTER XVII. 



1. How is the light produced in an incandescent lamp? 

2. Why is a vacuum necessary in the bulb of an incan- 
descent lamp? 

3. Why is it necessary to use so expensive a metal as 
platinum to carry the. current to the carbon filament 
throug-h the glass? 

4. What is the necessary condition of the voltage of 
supply to produce a bright light and a long life in an in- 
candescent lamp? 

5. How many watts are used in an ordinary 16-candle 
power incandescent lamp? 

6. When doe? it pay to destroy an incandescent lamp 
and substitute a new one? 

7. What is the temperature of the electric arc? 

8. How many watts per candle power are required in 
an arc? 

9. Why do the modern inclosed lamps give better illu- 
mination but less light than the old style open arcs? 

10. Why do the inclosed arc lights burn so much long- 
er t?han the open arcs? 

11. Describe the feeding mechanism in a consiant cur- 
rent arc lamp. 



^ 

i^ 



CHAPTER XVin. 



MEASURING INSTRUMENTS. 



There are a great many instruments used for measuring 
Tarious electrical quantities, but all that can be considered 
in this chapter are volt meters and ammeters of the more 
common type. 

Common volt meters are really ammeters with a very 
high resistance in circuit and so arranged that the current 
which passes through them is proportional .-Oo the voltage; 
therefore what the meter actually measures is the amount 
of current that passes through it, but as the cur- 
rent is proportional to the voM-age, the movemenits of the 
measuring instrument may be made to read volts direct. 

Fig. 71 is a diagram showing the way in which a Weston 
meter is constructed. This is an excellent illustration of 
the fundamental* fact on which the operation of motors de- 
pends. 

A permanent magnet M causes magnetic flux to flow 
across tihe gap G; situated in this gap is a bobbin B, on 
which are wound a number *of tunnis of copper wire. The 
bobbin is made of copper and is arranged to revolve on 
jewel bearings. Two springs S, one above and one below the 
bobbin, carry the current from the movable bobbin to the 
stationary part of the meter. If current is now passed 
through the bobbin by way of the springs, the current will 



208 



flow downwards on one side of the bobbin and upward on 
the other side. Thus the current in both sides of the bobbtn 
produces a torque which moves the bobbin against the force 
of the two hair springs S. The bobbin will continue to 
move until the torque exerted by the current equals the 
counter-torque exerted by the two springs. A pointer reg- 
isters the amount of motion and the position of the pointer 
is read off as volts. 




Figure 71 
Diagram of connections and moving parts of Weston voltmeter 



A little examination will show that the torque exerted 
by the wires carrying the current on bobbin B is propor- 
tional to the current, for the flux is constant throughout 
the whole air gap. It is also true that the counter-force 
exerted by the two hair springs is proportional to the move- 



209 



ment of the bobbin; therefore twice as much current in 
the wires on the bobbin will produce twice as much move- 
ment of the pointer over the scale. The magnet M is made 
of Tungsten steel and is artificially aged, so that when the 
instrument is turned out of the factory the magnetizing 
power of the magnet will remain constant for years. 




Figure 72 
Connection of Weston ammeter. 



Current is brought into the instrument through the 
binding j>osts A and C, but, before passing through the wire 
on the bobbin, the current must traverse the very high re- 
sistance R; this resistance is from 65,000 to 75,000 ohms for 
a volt meter intended for a 600-volt circuit. Therefore the 



210 



current whicl] passes through the wires on the bobbin, even 
with full voltage, is very small, and with 100 volts will be 
not much over 1-700 of an ampere. Yet this small current 
is ab]e to produce very considerable deflection in the two 
hair springs which resist the motion of the bobbin. An- 
other very excellent point in the design of this meter is the 




Figure 73 

Magnetic vane voltmeter depending on repulsion of two 
similarly magnetized iron strips. 



Tvay in which it is made deadbeat, or the way in which the 
needle is prevented from vibrating back and forth on each 
side of the point at which it will finailly come to rest. The 
bobbin B is made of copper, and when it moves there will be 
generated in it aurrents which, according to Lentz's law,tend 



211 



to prevent its motion. The mechanical momentum given to 
the bobbin by the action of the current in the wires thgt 
are wound on it is absorbed by these Foucault or eddy cur- 
rents in the copper bobbin. The Weston direct current me- 
ters are almost perfectly deadbeat. 




Figure 74 

Western electric meter depending on effort of iron strip to get into 

as powerful fielA as possible, or to get as near to the 

wire carrying current as possible. 

In Fig. 72 is a sketch of the Weston di- 
rect current ammeter. The working parts 'are precisely 
the same, the principle of operation is identical, and it 
would be impossible to tell the two dnstruments apart, 
so far as the actual indicating mechanism is concerned, if 
it were not that the bobbin is wound with coarser wire. 



212 



The wire on the bobbin is a shunt on the resistance 'R. The 
wiiole current to be measured passes through the meter 
from binding- post A to post C. In doing- so it has to pass 
through the resistance E. The voltage at the extremities 
of this resistance is, according to Ohm's law, proportional 




Figure 75 ^ 

Brush Electric Co. voltmeter and ammeter in which the attraction 
of a Solenoid for an iron core is weighed. 

to the current; or, looking at it in another way, the current 
will divide between the resistance R and the bobbin B in- 
versely proportional to their resistances. Therefore, when 
a large current is passing through H, d oorrespomdirigly 
iarge current is passing thrmigh bobbin B. As we have 



213 

seen in Fig-. 71, the posdtion of the pointer registers th« 
amount of current passing through the bobbin, fndTt wH 
be seen that the position of the pointer may be read off 
directly as amperes. 

..J.^^'^l "■^'" "* *^' ""'"P"" measuring instruments de- 
pend for their action upon the attraction of a solenoid for 







i 



214 

a piece of iron. The attraction of the solenoid is balanced 
by a spring or gravity and the position at which equilibrium 
occurs is a measure of the attracting force, and therefore a 
measure of the ampere turns in the solenoid. Whether the 
position of the pointer is to be read off as volts or amperes 
depends on whether the coil is wound with fine wire of 
coarse wire. 

A serious objection to these instruments in so far a9 
their accuracy is concerned, is that they will record highei 
Talues on descending amperes or volts than on ascending* 
This is due to the residual magnetism. When a current oi 
25 amperes would pass through the meter this would cause 
a certain number of lines of force to pass through the iron 
part of the meter. When the current sank to 23 amperes 
a certain number of lines due to the 25 ampere currenV 
would still remain in the iron, laind this number would b^ 
greater when the current would pass from 25 amperes io 
23 amperes than when it passed from 21 to 23 amperes. 
The mechanical force acting on the iron would be greater 
in the first than in the second case and therefore the am- 
peres indicated will be higher. Error due to this cause 
amounts to from 2 to 10 per cent., depending on the con- 
struction of the meter. Fig. 73 show^s one style of mag- 
netic vane meter. Fig. 74 shows the meter built by the 
Western Electric to. Fig. 75 shows a style of meter for- 
merly built by the Brush Electric Co. Fig. 76 shows the 
type af meter built by the Westinghouse Electric Co, 



215 



THOMPSON REiCORDING WATT METER. 



Mo&t of tihe recording meters in use in this country are 
of this type. In general, the meter is simply an ordinary 
motor, except that it is built without iron, as sihown in 
Fig. 77. Attached to the shaft of <this motor is a reftarding 
disc, which is made of copper and is revolved between per- 
imanent field magnets. The field coil in this meter is usu- 
ally made of coarse wire, and through it pa/sises the current 
to be measured. The armature i's wound up with fine wire 




( !^ 



^ 



^ •,<i'H'i>H 



Figure 77 

Diagram of connections and operation of Thompson's 

recording wattmeter. 

and is connected up to a sonall commuitator co-mposed of 
silver bars. Two thin silver brushes touch this comanuta- 
tor and carry the current to and from the armature. The 
torque on the motor is proportional to the product of the 
current in the fields and armature. In well regulated sys- 
tems, the voltage supplied is so nearly constant that the 
currenit in the armature is practically the same for any 
load. 



216 

It shoiiid be remarked that, in order fto reduce the 
ctirrent wasted in passing through the armature to the 
smallest possible amount, there is in series with the arma- 
ture a very large external resistance. The voltage supply 
being practically constant, the current through the arma- 
ture v^ll also remain constant. The only factor thait varies 
much is the current in the field. Eddy currents are gener- 
ated in the copper disc by its motion between the poles of 
the permanent magnets, and doubling the speed doubles the 
voltage produced and therefore doubles the current or quad- 
ruples the watts lost in the disc. 

In order to make the instrument register correctly, the 
speed must be twice as great w'hen 20 amperes are passing 
through the field as when only 10 amperes are passing 
through. 

Doubling the current through the field doubles the mag- 
netic field through which the armature revolves, and this 
doubles the torque on the armature. Doubling the speed 
doubles the current produced in the retarding disc, so that 
the increased torque is balanced by an equally increased 
resistance or counter torque in the disc. If the armature 
speed is doubled its counter electro-motive force will be 
quadrupled, because it is revolving at double speed in a 
field of double strength. 

Since in anj- case the counter electro-motive force is 
extremely small, the current passing through the armature 
5s not varied appreciably by the variation in the counter 
electro-motive force. We have then, by dou'bling the speed, 
quadrupled the watts lost in the revolving copper ring and 
at the same time have quadrupled the energy imparted to 
the armature by quadrupling its electro-motive fore© 



217 

against a constant current. Since these same relations al- 
ways hold, it is clear that the speed of the instrument will 
be alwaj^s proportional to the current passing- tTirough it. 
Consideraition will show .'that a change in the voltage while 
the current remains cooistan twill change 'the counter electro- 
motive force of the armature and its speed in the same way 
that change of current does. 

If the voltage alone should change and the current be 
constant, the same relation is true. Suppose the voltage to 
he doubled; the current through the armature would be 
doubled and there would be twice the torque on the arma- 
ture. This double torque would produce double speed and 
consequently double counter E. M. F. acting against double 
current, or it would exert four times as much energy as at 
the lower speed. 

Thus, for either case 'of change of volitage or current 
ihe sneed of rotation is a correct measure of the energy 
passing through it. 



15 



QUESTIONS ON CHAPTER XVIli;. 



T, What does a common volt meter really measure** 

2. On whart law doets 'the accuracy of tlli'e common voit 
meter depend? 

3. If, in Fig. 68, tbe righit-lia.njd pole is moo-tlh, which 
way does the current flow through the right-hand side of 
the bobbin w^hen the needle registers voltage? 

4. What makes the Weston volt meter dead beat? 

5. What is the object of the iron core between the 
poles of the horse-shoe magnet? 

6. WTien the meter registers the voltage and comes to 
rest, what tw^o forces are equal? 

7. On what does the permanent accuracy of this meter 
depend? 

8. What is the difference between tn.e Weston am- 
meter and volt meter? 

9. Describe the electrical connections in the ammeter. 

10. Describe the action of the magnetic vane instru* 
ment. 

11. Wliat is the objection to measuring instruments 
using soft iron? 

12. Wliy is the speed of the Thompson recording meter 
proportional to che watts in the circuit to which it is con- 
nected ? 

13. If the voltage of th-e circuit supplying the current 
is constant, and the power required to rotate the copper 
disc is proportional to the square of the speed, why will 
doubling the current double the speed? 



CHAPTER XIX 



ALTERNATING CURRENTS. 



The currents that have been previously considered in 
this v^ork have been direct; that is, constantly fiov^ing in 
one direction. An alternating current is one which changes 
its direction many times every second; that is, the current 
flows first in one direction and then in the opposite, the 
time required for alternation or reversal varying from 1-50 
to 1-275 of a second. In the older lighting dynamos the 
number of alternations usually employed was irom 250 to 
266 per second. Modern alternating current machinery op- 
erates from 50 to 125 alternations per second. 




Figure 78 
Two successive alternations or one cycle. 

Fig. 78 is the diagram of two successive alternations an 
a circuit. Two successive alternations, such as shown in 
this figure, are called a period or a cycle. A two-pole ma- 
chine will produce one cycle every revolution. Fig. 79 



220 



shows a bi-polar dynamo with a single coil wound on it, 
with the two ends of the coil connected to a pair of rings on 
which brushes make contact. As this coil revolves between 
the poles of the dynamo there will be a certain E. M. F, 
produced at each point. The E. M. F. will be a maximum 
when the coil is horizontal and the plane of the coil and 
plane of the poles coincide. From this point on the volt- 
age decreases graduailly until the coil is vertical, and at 
this point Decomes zero. As the coil moves on voltage is 






Fignre 79 
Alternating cuirent produced in a bipolar field. 



again generated, but now^ in the opposite direction. When 
the coil reaches the horizontal position the voltage will be a 
neo-ative maximum, wiiich graduahy diminishes until the 
coil has reached the vertical position again and the voltage 
sunk to zero. The voltage will now be produced in a posi- 
tive direction and again increased to a maximum. 



221 

A cycle is usually considered to begin at the point at 
which the voltage is at zero and at which the current which 
is to be generated in the next half revolution will be posi- 
tive. 

Fig. 80 shows -a coil revolving in a uniform field. Such 
a coil will generate w^hat is known as a sine wave; this is 
the form of the current w^ave that is sought in all power 
transmitting m-achinery, Flig. 78 shows the sine wave. 



^B 



^ 



Figure 80 
Coll revolving in uniform field and producing a sine wave. 



The old Westinghouse alternating current dynamos used 
for lighting were run at 133 cycles per second. The Thomp- 
son-Houston were run at 125 cycles per second. Most of 
the modern alternating current machinery is run at 7,200 
alternations per minute, or 60 periods per second. The 
great plant at Niagara Falls, which transmits power to 
Buffalo, runs at 3,000 alternations per minute, or about 25 
per second. An ordinary alternating current is called a- 
single phase current. Such a current as would be gener- 
ated in the mechanisan shown in i^'igs. 79 and 80 would be 
a single phase current. 



222 



A two-phase current is really not one current, but two 
separate currents produced from one dynamo. One of these 
currents succeeds the other in such a way that when the 
first current is at a maximum the other current is at zero; 
in other words, they are* a quarter cycle apart. 




Figure 81 
One current of a two phase current. 



7/ O* 9»' 




Figure 82 
The other current ic a two phase current. 



^g. 81 shows one of the currents in a two-phase dy^ 
nanio; Fig. 82 -shows the other. Fig. 83 show^s the two com- 
bined in one diagram. Fig. 84 shows a w^ay in w^hich a two- 
phase current may be taken from a direct current commu- 



^ 



2'^'6 



tator. It will be seen by an examination of Fig. 84 that 
the two currents which are taken from the commutator of 
the two-pole dynamo are connected to bars which are 00 de- 
grees apart; thus when the current in circuit No. 1 is at zero, 
the commutator bars to which it is attached are on a hori- 
zontal line and. there is no difference of voltage between the 



♦ MAX. ♦MA)t 




-MAX. -.>1AX 

Figure 83 
Diagram of two phase currents or Figures 81 and 82 on one diagram. 



///J. 



BRUSH 

RING 

INSUL' 




Figure 84 

Method of producing two phase current from the commutator 
of a bipoxctr armature. 



224 



two bars, and therefore there is no current in the circuit. 
The circuit No. 2 is attached to bars which are in a vertical 
line, and the voltage between these bars is at a maximum. 
Fig*. 84 makes it clear why it is that the iw^ currents in a 
two-phase circuit are said to- be 90 degrees apart. A three- 
phase current is one in which, there are three currents, but 
they can hardly be called three separate currents. If the 



•••MAX 




WAX 



Figure 85 
A diagram of the currents in a three phase line. 



three sliding rings shown in Fig. 86 be connected to three 
commutator bars 120 degrees apart on the commutator of a 
two-pole dynamo, the current which is taken from these 
three sliding rings is a three-phase . current, as 
shown in diagram in Fig. 85. Thus, if there 
were 36 bars in the commutator of a two-pole dynamo, one 
slide ring would be attached to commutator bar No. 1. The 
second slide ring will be attached to commutator bar No. 13 
and the third slide ring would be attached to commutator 
bar No. 25; or, each slide ring is attached to a point 1-3 the 
circumference of the commutator away from its neighbor. 
Since there are 360 degrees in a circle, these currents are 
said to be 120 degrees apart. If a two-phase current were 



226 



to be taken from this same commutator, circuit No. 1 would 
be attached to bars Nos. 1 and 19; circuit No. 2 wouM be 
attached to bars Nos. 10 and 28. By a proper combination 
of two-phase or three-phase currents it is possible to pro- 
duce a revolving pole. By placing inside of the apx)iaratus 
which produces this revolving pole a short circuited arma- 
ture, this will be dragged around by the revolv- 
ing pole in the same way that a short circuited armature 
in a direct current machine would be dragged around if the 
fields were revolved about such an armature. Such a ma- 
chine is called an induction motor. 



^I, ^'^\ ^3 




Figure 86 

iH^eUiod of producing three phase current from the commntatof 
of a bipolar armature. 



The great advantage that alternating currents possess 
over direct currents is that they can be transformed from a 
low voltage and a large current to a high voltage, and imiall 
current without any moving mechanism, or vice versa. 



226 



Alternating current is tistially generated for lighting 
purposes in a dynamo at from 1,000 to 2,000 volts. A small 
current at this high voltage will transmit a large number 
of watts, and only small wires will be needed to transmit 
this small current; one ampere, for instance, of this cur- 
rent at 1,000 volts is received in the primary coil of a trans- 
former, which changes it into 10 amperes at 100 volts, or 20 
amperes at 50 volts, depending upon the winding of the 
transformer. This low voltage current is distributed 




Figure 87 
Diagram of alternating current transformer. 



'through the building 'to be lighted and operates 20 incan- 
descent lamps. Fig. 87 is; a diagram of a transformer; P is 
the primary coil which receives the high voltage current, S 
is the secondary coil which delivers the low voltage current, 
I is an iron core passing through both coils. According 
to Lentz's law, current will be generated in the secondary 
coil in opposition to that of the primary. The number of 
turns on the primary and on the secondary coils is in the 
ratio of their voltages. Thus, if there are 100 turns on the 
primary coil and it is designed to receive current at 1,000 



227 



volts, there will be five turns on the secondary coil if it is 
desired to have it deliver current at 50 volts. 

The transformers are connected in parallel across the 
main circuit and the self-induction of the primary coil pre- 
vents excessive current from flowing" through it when 
the secondary circuit is open. Thus, suppose current is 
supplied at 125 periods per second and that there are 100 
turns on the transformer and that 2,000,000 lines flow 
through the core of the transformer on an average. A 
little study will show that the voltage produced in a coi^ 
having 100 turns placed around this iron core would be 

100x125x4x2,000,000 



100,000,000 

Solving this equatioin, ^Ye find that there will be 1,000 volts 
produced in such a coil. 

If 1,000 volts would be produced in a separate coil, 
there must be the same voltage produced in the coil which 
is attached tO' the 1,000 volt line wires. In this coil the 
vol/tage will appear as counter electro-motive force oppos- 
ing the voltage of the 'main circuit. This E. M. F. is al- 
most precisely equajjo the E. M. F. on the large line wires, 
and, in fact, the only current that leaks through the pri- 
mary coil is jus't enough to- produce ampere turns suffi- 
cient to cause 2,000,000 magnetic lines to flow through the 
iron core of the transformeir. 

When the secondary circuit is closed, however, the cur- 
rent in it tends to de-magnetize the iron core, because, ac- 
cording to Lentz's law, it flows in the opposite direction 
to that in the primary coil. There will be, therefore, a 
certain number of counter magnetizing turns due to the 
ciurent in the secondary coil, and there must be always 



228 

jusit e-nough more magn'etiziiig turns in the primary coil to 
overcome the de-magnetizing tuims in the secondary coil 
and still force the magnetic flux through the iron core, and 
so produce the counter E. M. F. in its own coils sufficient 
to oppose the E. M. F. of the main line. 

It will be noted that the transformer receives and de- 
livers the same number of watts, but that this number of 
watts may be made up volts and amperes in almost any 
ratio that we please by properly choosing tlie number of 
turns on the two coils. 3?he Ruhmkorff coil is an example 
of this, in which a battery current of a few volts and eight 
or ten Amperes is transformed into an exceedingly small 
current, but having a voltage of hundreds of thousands of 
volts. It is to be kept in mind that the battery current is 
interrupted or, in effect, made alternating by the circuit 
breaker on the coil. The alternating current system of 
transmitting power is without doubt destined to come into 
very extensive use on account of the ease of transformation 
with a transformer without any moving parts and on ac- 
count of the cheapness of the line over which the power 
can be efficiently transmitted after being transformed with 
such little expense. Lines are in use in this country in 
w^hich power is transmitted 40 miles at a pressure of 40,000 
volts. In an experimental plant in Germany power was 
transmitted 130 miles with a loss in the line amounting to 
only 13 per cent. Without doubt power electrically trans- 
mitted by alternating currents of high voltage is destined 
to play a very large part in the industrial development of 
this country. 



QUESTIO^s^S ON CHAPTER XIX. 



1. Wihat is an alternating current? 

2. How many alternaitions per second were used in the 
older lig*hting systems? 

3. What is a period? 

4. A four-pole machine is running 1,100 reTolutionp 
per minute; if it is producing alternating current, iiow 
many cycles per second will this current have? 

5. How may an alternating currenl: be produced from 
an ordinary direct current motor or dynamo? 

6. What is a sine wave? 

7. What is a single phase alternating current? ^ 

8. What is a two phase alternating current? 

9. If a two phase current is taken from a direct cur- 
rent two-pole dynamo, to what points on the commutaitor 
will the four rings be attached? 

10. What is a three phase alternating current? 

11. How may a three phase current be produced from 
a direct current two-pole dynamo? 

12. Why are the currents of a two-pha^e current said 
to be 90 degrees apart, while the currents of a three-phase 
current are said to be 120 degrees apart? 

13. If possible, sketch the connections which would be 
necessary to produce a revolving pole with a two-phase cur- 
rent. 



230 

14. What advantages do alternating currents iiave over 
direct currents? 

15. What is an alternating current transformer? 

16. What is the object of a transformer? 

17. How is current produced in the secondary coil 
from a primary coil with insulation of thousands of ohms 
between the two coils? 

18. Why will a transformer connected across a thou- 
sand-volt circuit and having a resistance of only one ohm 
allow only a small part of an ampere to pass? 

19. Why will the current in the primary coil increase 
vvhen the resistance of the secondary circuit decreases? 

2Q. What is true of the watts received by the primary 
cofil and the watts delivered by the secondary coil? 

21. What is a Rhumkorff coil? 

22. Why is the alternating system of power transmis- 
sion rapidly coming into use? 



CHAPTER XX. 



ELECTRIC AUTOMOBILES. 



The practicability of the electric automobile was long ques- 
tioned, because of the severe duty imposed on the storage bat- 
tery; with the many improvements in the latter, which have 
taken place in the last few years, however, the development of 
the electric automobile has taken rapid strides, until to-day 
it stands in the front rank of automobiles. Batteries are now 
manufactured practically *'fool proof" and of capacity to run 
a vehicle under ordinary conditions 35 miles or more on one 
charge. The medium for transmitting the power or the 
Electric Motor is ideal for this purpose ; it is simple in con- 
struction, it is efficient, and it has a rotative movement which 
insures smooth running, free from vibrations of any kind, and 
Tt is easily controlled. 

There are principally two systems of Electric Automobiles : 
the one using a double motor equipment with each motor driv- 
ing a rear wheel through gearing, and the other employing a 
single motor which is connected by gearing or chain to a 
differential gear driving the rear axle. The two systems have 
each their advantages, but are in principle the same, though 
the single motor equipment is probably the one most extensive- 
ly used. 

The equipment of an Electric Automobile consists of the 
motor, the controller anc?" tjie storage battery. 



282 
THE MOTOR. 



The automobile motor, being exposed to all sorts of 
weather conditions, as well as liable to all sorts of abuse, 
must be particularly designed for these conditions. Also as 
the source of power, the storage battery, used in an automo- 
bile, must be kept down as low as possible on account of its 
comparatively great weight; the design of this type motor 
requires the greatest care and experience. The principal points 
to bear in mind when designing an automobile motor are that 
it must be weather-proof and accordingly entirely enclosed, it 
should be as light in weight as possible, it should have a 
large overload capacity and a good efficiency over a wide range 
of loads. 

As in street car service, the power required for starting is 
very large as is also the power required for climbing hills, 
and for this reason the same type motor has been selected for 
automobiles, that is, the series motor. In this motor, the fields 
being connected in series with the armature, the same current 
will flow through both, therefore the torque of the armature 
will be proportional to the square of this current. According- 
ly, when starting the motor, the armature then being at rest, 
there will be no counter electromotive force to oppose the 
current flowing, this current will be comparatively large and 
the torque great. In the same way when climbing hills the 
speed will be low and the counter electromotive force low and 
the torque large. After the start, and when running on a level 
road, the torque required is small and accordingly the current 
small and the speed high. 

In point of efficiency, however, the automobile motor dif- 
fers in design from the street car motor, the work of the 
automobile motor being a great deal more uniform, that is, 



233 



it is not called upon to render as frequent overloads or as 
frequent changes in load as the street car motor, but is run 
at a fairly constant load most of the timiC. Accordingly, the 
fixed losses are kept as low as possible, that is, losses due to 
hysterises and eddy currents in the armature iron, brush fric- 
tion and bearing friction. 




Figure 88 
Outline drawing of automobile motor. 



In mechanical design, the automobile motor practically 
stands as a type of its own. It is made "fool proof,[' dust 
p^oof and weather proof, and all working parts that generally 
need attention are made most simple in construction so as to 
require the least amount of care. Ball bearings are used 
throughout, reducing bearing friction to a minimum, but in- 
creasing the life of the bearings, though requiring very little 
care. 

For reasons of keeping the weight down to the lowest 
possible for the largest output, the utmost care should be exer- 
cised in the distribution of the material needed, as well as 
the selection of same. 

16 



s ^ 




*^ 'I ^1 -I 'I ^1 ^t i 1 ''I ^^ '^ "« *^ 



^)^ 
^ 



235 

The magnet frame is usually of cylindrical shape of small 
diameter, resulting in a compact design; its material is cast 
steel or wrought iron forging and sometimes laminated steel 
built up in the same manner as the armature core. The end 
housings, which contain the ball bearings, are cast of alum- 
inum ; only the commutator end housing being supplied with a 
small water-tight lid which enables examination of commuta- 
tor and brushes. Fig. 88 shows the outlines of a small auto- 
mobile motor, illustrating in a general way the principles em- 
bodied in its design. 

The horse power required to propel a carriage weighing 
(w) tons at a speed of (v) miles per hour on a grade of (p) 
per cent, or number of feet rise or fall respectively in a length 
of lOo feet, may be found from formulae 

w X (50 4- 20 X p) X V 

H. P. eouals 

375 

In Fig. 89 this formuxae has been used in calculating the 
power required to propel a vehicle weighing 1,000 lbs. or Y^ 
ton at various speeds and grades from 0% or level to 20%. 
The same Fig. 89 also gives revolutions per minute of various 
sizes of driving wheels most commonly in ase. 

To illustrate the use of these curves, we will assume a 
carriage weighing 1,500 lbs. and desire to know the amount of 
power required for this carriage climbing a hill of 8% grade 
at a speed of 16 miles per hour. • 

From above formulae we have : 

i§H(50 + 20x8)xl6 

H. P. equals equals 6.75 . 

• 675 

This would have been found from the curves in the fol- 
lowing way: The horizontal line marked 16 miles per hour 
intersects the diagonal line marked 8% at a certain point : from 



236 



this point follow a vertical line down, and read off the result, 
which is 45 H. P.; this is, however, for a vehicle weighing 
1,000 lbs., and as the carriage in our example weighs 1,500 lbs., 
the above result must be multiplied with 1.5, which gives us 
6.75 H. P. as before. In the same way, if our vehicle has 30" 
driving wheels and it is desired to know the revolutions per 
minute of the horizontal line marked 16 miles per hour, con- 
tinue the horizontal line marked 16 miles per hour until it 
intersects the diagonal line marked 30" wheel; from this 
point follow a vertical line upwards and read the result, which 
gives us 180 revolutions. From this the proper gearing be- 
tween motor and driving axle may be selected. 







•S • E ■ 6 B-^-Q-B-g • B 









1 - 



iTTin 



? — 




AV^»^- 



Figure 90 
Diagram of controller connections. 



237 
THE CONTROLLER. 

The automobile controller is generally of the drum type, 
having one large drum with contacts arranged for two or 
three speeds and on small drum for reversing; in some types 
of controllers the two are combined in one single drum ope- 
rated by a handle placed in some convenient position under 
the seat of the carriage. 

Fig, 90 shows a diagram of controller connections for a 
vehicle motor using a single motor and is arranged for a 
separate reversing drum and a speed drum giving three speed 
positions and one charging position. All contacts marked with 
the same number are electrically connected. In the diagram 
contacts illustrated on the dotted lines i, 4, 5, 6, all belong to 
the speed drum and must be considered moving together, as 
this drum is rotated. In the same way contacts illustrated on 
dotted lines 7 and 8 belong to the reversing drum and rotate with 
this drum. Further, contacts on dotted lines 3 and 9 repre- 
sent springs or controller ''fingers" which are stationary and 
permanently connected to the various apparatus, as batteries, 
motor, etc. Suppose the reversing drum to be in the position 
of "ahead" that is moved so that the dotted line 7 is under the 
dotted line 9, and further that the speed drum is moved to the 
position of "ist speed" or so that the dotted line 4 is under the 
dotted line 3, and we trace out the connections thus estab- 
lished, we find that the current from the four sets of batteries 
unite, flowing through the watt meter or combined ampere and 
volt meter, thence through the circuit breaker or fuse through 
the series f:eld of the motor, the armature and back to the 
speed drum, there splitting to the different batteries. We 
have thus a parallel connection of the batteries or the lowest 
voltage available; if the capacity of the storage battery when 
connected in full series is 80 volts, we would have 20 volts at 
the terminals of the meter with the controller in this position. 



238 



By similarly tracing the connections for other positions, the 
2nd speed position will give us a series parallel connection of 
the batteries or a voltage of 40 at the terminals of the motor, 
and, lastly, the 3rd speed position gives us the straight series 
connection or the full voltage of 80 at the motor terminals. 
When the speed drum is on the charging position the motor 
is entirely disconnected and the batteries arranged in full 
series, connected through the meters to the charging terminals. 
The particular controller just described had a brake attach- 
ment applied to the controller handle whereby with one move- 
ment of the handle power might be turned off and brake ap- 
plied; this position is marked in the diagram by dotted line 
2 as "maximum brake." Such an arrangement has the advan- 
tage of being less confusive than the employment of a separate 
brake handle, especially rn emergency cases where quick stops 
are necessary and the time which would be lost in fooling with 
separate handles as a rule is very valuable. 



THE BATTERY. 



The automobile storage battery does not, in principle, 
differ from the stationary storage battery; it is a lead battery 
formed according to the Plante or the Faure method. The 
Plante process, which was briefly mentioned under Chapter IT, 
requires for the complete formation of the battery a repeated 
reversal of the current and is very tedious and expensive. 
By treating the plates with certain acids, however, the forming 
may be accomplished in a comparatively short time. The 
Faure process consists of applying or pasting already formed 
materials to the lead plates. The materials used for this 
purpose are red lead and litharge mixed with sulphuric acid 
and water to make a paste; plates made up in this manner 



239 



need then simply be charged to be ready for use. In both 
cases the electrolyte used is diluted sulphuric acid. 

In the following we will make a brief description of the 
Chloride, the Willard and the Edison auto-batteries as being 
of three distinct types in regard to construction and forma- 



tion. 



THE CHLORIDE ACCUMULATOR. 

The positive plate of this battery is cast of lead in the 
shape of a grid whose perforations are round holes some- 
what less than M" in diameter and about i" between centers; 
these holes taper to a smaller diameter from the outside sur- 
face to the middle of the plate, making, in fact, countersunk 
holes from both surfaces of the plate. The active material 
consists of pure lead in the form of ribbons, the width of 
which are equal to the thickness of the plate. These ribbons 
are wound into spirals which are pushed into the holes of the 
grid. The negative plates are made by casting under heavy 
pressure around pellets of active material placed in the mould, 
a grid of an alloy of lead and antimony. The pellets are made 
of finely powdered lead dissolved in nitric acid; by adding 
hydrochloric acid to this solution a precipitate of lead chloride 
results. This precipitate after being washed is then melted 
with zinc chloride and poured intb moulds to ^orm the pellets, 
which are about 54" square and of the same thickness as the 
plate. The finished plates are then placed between zinc 
plates and immersed in a zinc chloride solution; the electro- 
chemical action resulting from short circuiting these plates 
are to remove the chloride, leaving the pellets in the form of 
pure lead in a highly porous state. 

There are several types manufactured, of which the fol- 
lowing are examples : 



240 

TABLE XXII. 
ELEMENTS OF TYPE M. V. 



Number of Plates: 


5 


7 


9 


'' 


13 


15 


Discharge in amperes for 
3 hours. 


18 


27M 


S6H 


45M 


55 


64 


Weight in lbs. of com- 
plete cell with electro- 
lyte. 


19^8 


28 


36 


44^ 


53K 


61H 



THE WILLARD BATTERY. 



The plates of this battery are of the Plante type and are 
made up of lead sheets ridged or grooved across the whole 
width of the plate ; the grooves are cut in a downward direc- 
tion from the surface of the plate to its center, thereby form- 
ing V-shaped pockets or shelves which greatly increase the 
active surface of the plate and after forming serve to retain 
the active material. It is claimed that the Willard plates 
are not subject to any deterioration or buckling as the active 
oxides when formed between the ribs, by their expansion, only 
cause these thin ribs or shelves to open up and slightly 
separate from each other. The internal resistance of this 
cell is very low as its construction gives a plate without any 
joint whatever between the active and the conducting ma- 
terials. The positive and negative plates in each cell are 
separated by hard rubber discs which are perforated to allow 
free circulation of the electrolyte. 

Following are two tables giving some data of the Willard 
batteries : 



241 

TABLE XXIII. 
WILLARD STANDARD BATTERY. 



Weight in 


Ampere Hour Capacity when Discharged in 


Pounds. 


3 hrs 


4 hrs. 


5 hrs. 


6 hrs. 


13 


34 


38 


40 


42 


16 


45 


50 


53 


55 


19 


56 


63 


67 


70 


22 


66 


73 


78 


81 


28 


84 


93 


99 


103 


35 


112 


124 


132 


137 



TABLE XXIV 
WILLARD SPECIAL BATTERY. 



Weight in 


Ampere Hour Capacity when Discharged in 


Pounds. 


3 hrs. 


4 hrs. 


5 hrs. 


6 hrs. 


18 


48 


53 


56 


59 


25 


72 


80 


85 


89 


31 


96 


106 


112 


117 


37 


120 


132 


140 


147 


44 


144 


158 


167 


175 


50 


168 


180 


196 


205 



THE EDISON STORAGE BATTERY. 



The batteries described in the foregoing were all lead-lead 
batteries. The Edison battery is distinctly different from these 
in that it employs no lead whatever in its construction. The 



242 



plates are made up of steel and nickel, each individual plate 
consisting of 24 little cups or pockets pressed of thin steel 
heavily plated with a coat of nickel, which is afterwards fused 
to the steel. These little cups, which are made in two sec- 
tions, one engaging within the other like a capsule, are filled 
with the active materials — consisting of specially prepared 
oxides of nickel and iron — are placed in corresponding open- 
ings in a thin grid and the whole is subjected to a very high 
pressure. This locks the two sections of each cup firmly 




Figure 91 

Finished Plate, Grid and Group of pockets containing 
active material. 



together and fastens them securely to the grid. Fig. 91 shows 
the construction of aiT Edison plate. This construction results 
in an extremely strong and light plate, having good electrical 
contact between active and conducting materials. 

The finished cell consists of a number of such plates 
loaded with nickel oxide alternating with plates loaded with 



243 



iron oxide; the nickel oxide plates form the positive pole and 
the iron oxide plates the negative pole of the cell. To prevent 
the plates from coming in contact with each otlier, hard rub- 
ber rods are placed between same and sheets of hard rubber, 
as well as rubber supports, are used to separate the plates from 
the containing jar, which is made of steel in this battery. The 
electrolyte used is a 20 per cent solution of potash. 

The Edison battery is made m three sizes, of which data 
is given below : 

TABLE XXV. 



Type of Cell: 


E-18 


E-27 


E-45 


Capacity in ampere hours 


105-115 


105-115 


260-280 


Average discharge voltage per 
hour 


1.25 


1.25 


1.25 


Rate of discharge in amperes 


30 


45 


75 


Satisfactory rate ot charging in 
amperes. 


40 


65 


100 


Suitabl timeof charging in hours 


3K 


m 


334 


Weight in pounds per cell in- 
cluding so ution 


13 


i:k 


28 



The manufacturers claim that any desirable rates of 
charge and discharge may be employed without fear of injury 
to the cell. 



THE CHARGING OF AUTO BATTERIES. 

The voltage per cell of the lead batteries — which is as yet 
the most extensively used — is about 2 volts and it should never 
be allowed to discharge below 1.8 volts and rather not below 
1.9 volts. 



244 

When we wish to charge an automobile battery, we must 
first make sure of the charging current available, the voltage 
of the same, whether direct or alternating current, and if 
direct current, whether arc or incandescent. The next im- 
portant point to establish is the polarity of the terminals of 
our charging circuit as the positive and negative terminals of 
the same must be connected to corresponding terminals of 
our battery. On the battery the poles are usually marked with 
a + or ■ — and to ascertain the poles of our charging circuit 
we may connect the two terminals of the same to two lead 
plates immersed in a crock containing water and a little sul- 
phuric acid. The lead plate which turns brown is the one 
connected to the positive terminal and this is the one which 
must be connected to the terminal marked -{- on our battery. 
The other lead plate will take on a bluish color and is the 
negative terminal. 

If a series arc circuit is available and the battery consists 
of 20 to 30 cells, connect as per diagram. Fig. 92, where A-A 
is the 



^ 



H-^ 



Figure 92 
Auto charging connections for arc circuit. 

arc circuit, B is the battery terminals on the carriage, and C 
is a crock or small wooden trough containing water and some 
sulphuric acid. By varying the distance of the two lead plates 
in the crock, any desirable charging current may be had. The 
current and voltage taken is read off on the meters in the car- 
riage. 



245 

If the battery consists of 40 or more cells connections 
should be m.ade as shown by the dotted lines in Fig. 92. 

Should the charging circuit be a no volts incandescent, 
connections should be made as in Fig. 93, which may be 



F^ 



Figure 93 
Auto charging connections for incandescent circuit. 

used for any number of cells. 

If the only charging current available is alternating, it 
will be necessary to use a rotary transformer or some other 
apparatus for rectifying of the current, as storage batteries 
cannot be charged directly from alternating current. 

As there are several points of importance to take into ac- 
count when dealing with storage batteries, we will in the fol- 
lowing lay down a few general rules in the caretaking of the 
same, and also discuss some of the principal troubles which 
might be encountered. A battery should never be discharged 
below 1.8 volts at the very most and better not lower than 1.9 
volts ; when this voltage is reached the battery must be re- 
charged, the charging-voltage per cell to be from 2.4 volts to 
2.6 volts. If while recharging the cells should get hot and the 
electrolyte boil, the charging current should be reduced. 
Should it be -desired to charge rapidly the current may be 
started at a high value and gradually tapered off as the 
charging proceeds. For a three-hour charge, for , example, 
charge with 50% of the total current during the first hour, 
33^4% during the second hour and i6j^% during the third 
hour. 



246 



The battery should never be allowed to stand discharged 
for any length of time : when not in use give it a short charge 
about once a week. If it is to be laid up for a longer period, 
charge fully, take out the plates and wash and dry them thor- 
oughly. 

After a battery has been in use for some time part of the 
electrolyte has been lost through spilling or evaporation, and 
it must be replenished to such an extent as to always stand 
somewhat over the tops of the plates, about Yz" or so. Either 
solution or only water is added until the density of the electro- 
lyte reaches i.i to 1.2 and it should never be allowed to ex- 
ceed 1.26, as this may cause corrosion of the grids. The 
density is measured by a hydrometer on which it may be read 
off directly. Fig. 94 shows a hydrometer made especially for 
use with automobile batteries, which are always covered. The 
hydrometer proper is enclosed in a syringe ; 




Figure 94 
Automobile Hydrometer. 



if the tip of this syringe is inserted in the vent hole in the 
cover of the cell and the bulb compressed, enough electrolyte 
will be drawn up into the syringe to float the hydrometer and 
the density may be read through the glass tube of the syringe. 
The electrolyte is made up of about one part sulphuric 



247 

acid to six parts distilled water, By measure. When mixing 
the solution it must be remembered to pour the acid into the 
water, and never vice versa; if it be desired to add more water 
to the solution introduce same at the bottom of the cell by a 
tube or small hose. 

A common trouble with batteries is buckling of the plates; 
this is mostly caused by sulphating. A white sulphate of lead 
is formed between the supporting grid and the active material 
and if excessive will cause an expansion of the {)late, buckling 
or warping same. If sulphating should be discovered before 
buckling has already set in it may be cured by charging of the 
battery at a somewhat higher rate than usual, urtil the cells 
emit gas. A battery which is allowed to stand idle for a long 
time without being charged will invariably sulphate ; an over- 
discharge will cause the same trouble; this discharge may be 
through over-load or through short circuit between the in- 
dividual plates. 

Short circuit between the positive and negative plates in a 
cell is another common trouble which most always .is caused 
by active material shedded from the plates ; the only remedy 
is to remove the cause of the trouble. 



248 



QUESTIONS OX CHAPTER XX. 

1. What causes vibrations in other automobiles— not elec- 
tric ? , 

2. Is there any other automobile motor besides the elec- 
tric which has a rotative movement ? 

3. :Mention some advantage of single motor equipment 
over double motor equipment. 

4. ^Mention some advantage of double motor equipment 
over single motor equipment. 

5. Explain the reason for using a series motor for auto- 
mobile work. 

6. Required, the horse power necessary to propel a car- 
riage weighing 2,oco lbs. when running on a level road and at 
a speed of 12 miles per hour. 

7. What is the revolutions per minute of the driving 
wheels for carriage m example 6, if diameter of wheels is 36 
inches? 

8. What is the speed of the motor in example 6, if the 

gearing is 8:1? 

9. If a carriage is running at a speed of 20 miles per hour 
with controller in position of full voltage on the motor, what 
will the speed be with controller in ist and 2d speed position it 
conditions otherwise remain the same? 

10. If the hydrometer registers a density of 1.3 what 
should be done? 

11. Describe the color of the plates in a storage cell. 

12. How does the color of the plates change with dis- 
charge of cell? 

13. How are acid fumes from batteries neutralized and 

acid spots on clothes removed? 

14. How may *'sulphating" of a battery be prevented or 
sulphate removed? 



ANSWERS TO QUESTION'S ON CHAPTER I, 



1. Nothing of its ulimmate nature. 

2. They are probably better understood than, the laws 
gioverning heat land light. 

3. The operation of an hydraulic system. 

4. (a) The water pressure or head, (b) The amount 
of flow or number of gallons per minute, (c) The frietion- 
al resistance of the x>ipes oarrying the water. 

5. The volt. 

6. To one foot of head or pressure. 

7. The ampere. 

8. The ohm. 

9. Amperes equal volts divided by ohms. 

10. Ohm's law is only the application of a general law 
to electrical action. The How of heat thi*ough a wall is an 
example. 

11. About two. 

12. Usually 110. 

13. (a) One-«half ampere, (b) From six and a half to 
ten. 

14. One ohm. 

15. Loss of pressure bert:.ween boiler and engine in 
steam pipes. 



250 



16. On the amouiit of fluid carried iiirongh tJhe pipe 
and on the straig^tness and general character of the pipe 
line. 

17. To tihe dj'namo. 

18. To be filled in by student. 

19. Upon the amount of current transmitted and on 
the resistance of the wire. 

20. Draw a diagram and compare with Fig. 4. 

21. From 95 to 98 per cent. 

22. It is the loss of voltiage due to the resistanae of the 
wires over wMch the current niu!^t travel. 

23. The use of wires of such size that t4ie loss of voltr 
age shall be practically zero. 

24. On account of the great size of conductors needed 
and the consequent expense. 

25. To select wire of such size that tihe lamps shall at 
all times receive the same voltage. 

26. See text, page 8. 

27. No. (2). 

28. Write out and compare with text. 

29. Four volts. 

30. Such a circuit would require 800 feet of No. 0000 
wire. 

31 > I'ifty amperes. 

32. .077 ohms. 

33. 108 volts. 



251 

< 

34. 12,100. 

35. Abou't two vdlts. 

36. Wire twice ais large as No. 0000. 

37. So as to reduce 'the drop to as small an anDount as 
possible. 

38. $806.00. 

39. A'Mien only a few lamps are bnrning- on a distanrt 
circuit, the voltage on this circuit is practically that of 
the dynamo, and tends to burn out the lamps. 

40. Table 2, page 16. 

41. At least 50 volts. 

42. Through the rails and ground. 

43. Because the copper used in bonding t.he track is 
not nearly so great in amount as that required by the trol- 
ley wires and feeder. 

44. 2.50 times the size of a No. 0000 wire. 

45. $1,900.00. 

125 

46. x500 equals 833. 

75 

47. $1,141.00. 

48. No. 1 lor No. 0. 

49. SucJh a sj'Sftem would leave the trolley wire discon- 
nected near the power house. Power would be supplied to 
the line from the dynamos by feed wires connected at a 
distance from tiie power station. 



252 



50. By the oonstanrt: pot-en'tiial amd oonstaiut current 
systems. 

51. For operating the older arc lamp systems. 

52. Each device for receiving electricity ds exposed to 
the same electro-motive force. 

5ii. Each device for receiving electricity must carry the 
same current. 

54. From 9^^ to 10 amperes. 

55. About 6^2 amperes. 

56. The resistance of the wire in ohms equals 10 8-10 
times the length in feet divided by the square of the diam- 
eter of the wire in thousandlths of an incn. 



ANSWERS TO QUESTIONS IN CHAPTiJR 11. 

1. Galvani and Volta. 

2. Write the answer and compare with the text. 

3. From the negative plate through the outside circuit 
to the positive plate. 

4. The chemical action of the electrolite upon the posi- 
tive plate. 

5. The counter electro-motive force caused by the pro- 
duction on the negative plate of some gas, usually hydrogen. 

6. The positive element is the one on which the elec- 
trolite acts cheraiaally; the negative element Is -the remain- 
ing one upon which the electrolite has less or no chemical 
action. 

7. The terminal on the negative plate from which the 
current flows into the outside circuit. 

8. Platinum, carbon and silver. 

9. Because zinc and carbon are farther apart in the 
electro-chemical series than zinc and copper. 

10. Both mechanical and chemical means are employed. 
The mechanical means consists of blowing air or some other 
gas across the negative plate, or of providing numerous 
small points from which the gases may escape. 

11. Write the answer and compare with text. 

12. They cost too much. 



254 



33. Write description of Jablockoff battery and com- 
pare with text. 

14. Write description of plunge battery and compare 
with text. 

15. It should be amalgamated 

16. Directly proportional. 

17. An instrument in which the amount of current that 
has passed in a given time is measured by the amount of de- 
composition effected. 

18. Write answer and compare with text. 

19. An anode is the plate or electrode by which cur- 
rent enters the solution. A cathode is the plate or electrode 
by which current leaves the solution. 

20. With it. 

21. Write answer and compare with text. 

ELECTRO-PLATING. 

1. Metal is taken from the anode and deposited in a 
thin even layer on the cathode or work to be plated. 

2. See text. 

3. On the ampere hours or on tlie amount of current 
flowing multiplied by the length of time it flows. 

4. The work is burned. 
6. Yes. See text. 



255 
STORAGE BATTERIES. 

1. A storage ba'ttery is one in iwhich electrical energiy 
is consumed in producing* chemical change and which will 
return the energy so stored as electrical energy upon de- 
mand. 

2. See text. 

3. It does no>t polarize, has a very low resistance, and 
so is capable of producing heavy discharges, and has a high- 
er voltage than most primary batteries. 

4. For running horseless c|arriaiges and electric launch- 
es, and for absorbing the energy of a dynamo or circuit at 
times of light load and restoring it at times of heavy load. 
A battery may be very advantageously placed at or near the 
end of a long feeder line, so as to make the current that 
flows over the line nearly constant. 



ANSWERS TO QUESTIONS ON CHAPTER HI. 



1. It is magnetized. 

2. A small magnet is supported in such a manner 
as to be free to turn in a horizontal plane. 

3. A north pole is one that points to the geographical 
north. A south pole is one that points to the geographical 
south. 

4. The region of magnetic influence surrounding the 
poles of a magnet. 

5. From the north pole into the air into the south 
pole and through the iron to the north pole. 

6. The figure formed usually by iron filings in a field 
of magnetic force, showing the direction and intensity of 
magnetic force. 

7. It is much more concentrated than that of a bar 
magnet. 

8. See text. 

9. The circular and concentric lines surrounding a 
wire carrying a current. 

10. The same as between the direction of rotation of a 
righl hand screw and its direction of motion forwarrl oi 
backward. 

11. Up. 

12. South. 

13. North* 



257 



14. A piece of magrnetic metal around which, a current 
is circulating. 

15. See text. 

16. That end of an electro-magnet around which the 
current circulates in the direction of motion of the hands of 
a watch, as seen by the observer, is the south pole. 

17. Yes. The lines of force flowing from the electro- 
magnet may be considered as the sum of the magnetic 
whirls of the wires which surround the core. 

IS. A coil of wire in w^hich a current flows. It is a 
weak magnet. 

19. An electro-magnet without a metallic or iron core 
would be a helix. 

20. Tt expenences a mechanical force that pulls it side- 
ways across the magnetic lines. 

21. Current and fieldin proper relation are supplied 
and motion results. 

22. Motion and magnetic field properly related are sup- 
plied and electro-motive force which may produce a current 
is the result. 

23. Thumb, first and second fingers of the right hand 
are extended at right angles to each other, and point in the 
directions respectively of motion, lines and current. 

24. Extend the thumb, first and second fingers of the 
left hand at right angles to each other, and they will point 
respectively in the directions of motion, ISnes and current. 

25. "Because the direction of lines would be reversed 
without reversing anything else. 






258 



26 The wire on top moves in one direction, tlie wire od 
tbe bottom in the opposite direction, both of which tend to 
produce rotation in one direction. 

27. Current will tend to flow from the top to the bot- 
tom of the wheel. 

28. Current will flow in the direction of the hands of 
a watch, as seen by the observer on the south side of the 
loop. 

29. Current will flow from east to west. 

30. Current flows away -from the observer. 

31. About 1-10 of a pound per foot. 

32. 100,000,000. 

33. Yes. To provide sufficient friction between the 
wire and the armature core to prevent the wires moving 
from the mechanical force exerted between the current in 
the wire and the magnetic field. 



AiNSWERS TO QUESTIONS ON CHAPTER IV 



1. On tihe a.mpe<re turns. 

2. Yes. The relation between magnetic flux, ampere 
turns or magnetic motive force and magnetic reluctance is 
the same as that between current, electro-motive force and 
electric resistance, as given by Ohm's law. 

3. The flux corresponds to the current, the ampere 
turns or magnetac motive force to the electro-motive force. 

4. Directly proportional ito the lengi^h of the circuit 
and inversely proportional to its area. 

5. It multiplies the number of lines passing* throug'h 
the helix. 

6. Because all the ma^gnetic lines must pass throug'h 
the center of 'the helix and the area is restricted while the 
return path for the mag-netic lines outside the helix is 
practically unlimited. 

7. Flux equals ampere turns x area divided by length 



1425x7.07 

X.3132 equals equals 5850. 

5yoX.3132 



21 

— x5850 equals 8190. 

15 



250 



9. The multiplying' power of 3 magnetic nietal for 
mag'netic lines. 

10. Because tlie permeability is not constant. 

11. When it is carrying a great many magnetic lines. 

12. It is said to be saturated. 

13. In order to reduce the magnetic reluctance suffi- 
ciently to allow enoug-h lines of force to pass to produce 
the proper E. M. F. 

14. By comparing the number of masmetic lines that 
actually do flow through iron with the number that would 
flow through the same space occupied by air. 

15. They are about equal. 

16. It is a representatdon of one sample, but only ap- 
proximately represents the class. 

17. Wrought iron has about twice the permeability of 
cast iron. 

18. Because the permeability of each part is different 
and it is easier to get the desired result by making the 
separate calculations. 

19. 3371. 

20. A. t. in adr gap 2595 

A. t. in body of teeth. 100 

A. t. in neck of teeth 103 

A. t. in armature 495 

A. t. in pole piece 22 

A. t. in yoke 56 



261 

21. A. t. in adr g-ap, 2770 
A. t. in body of teeth, 240 
A. t. in neck of teeth, 200 
A. t. in armature, 38 

A. t. in pole piece, 49 # 

A. t. in yoke, 105 

22. Because the larger number of ampere turns is ex- 
pended in the air gap and an error in this calculation would 
make a great difference in the result, while the same error 
in the calculation of the yoke, for instance, would not make 
nearly the same difference. 

23. About one-half. 

I,000,000x37.68x.3132 

24. A. -t. equals equals 3970. 

9.62x309 

25. Nickel and cobalt. 

26. No. 

27.* One in whidh the wire is wound on the surface. 

28. They give mechanical support to the armature 
wires and greatly reduce the reluctance of the air gap. 

29. The lines tend to pass from the surface of the p«le 
piece in tufts or bunches. 

30. 12x(.310+-.062)x5 equals 22.32. 

5000xlx.3132 

31. A. t. equals equials 783. 

%x4 



262 



32. From 125,000 to 140,000 lines per square inch. 

33. It will reduce the flux six or eig-ht per cent. The 
exact amount of reduction could only be determined by- 
making several gn esses and figuring- oujt each one. If we 
assume *that it will decrease the flux 6%, figure out how 
many a. t. would be required in the imagnetic circuit for 
this number of limes, and, if nolt right, make a second or 
third. 

34. Because the permeability of the air gap while great 
is constant, while the permeability of the iron part of the 
circuit depends very greatly on the amount of flux. 

35. JBecause it is practically impossible to obtain exact- 
ly correct permeability values. 



AT^SWERS TO QUESTIONS ON CHAPTER V. 



1. One of the results of the flow of magnetic lines of 
force, usually exerted across an air gap between two pieces 
of iron. 

2. About 1,000 pounds per square inch. 

3. Because it increases the amount of flux across the 
air gap and does not produce enough to saturate the iron 
parts of the circuit. 

4. Because the pull is proportional to the square of the 
number of lines per square inch, and if the same flux can be 
crowded down to a small area the total pull will be increased 

5. The magnet will be one foot in diameter if 'it is to 
be as light as possible, for a given area of contact can be 
secured with less weight in a magnet of large diameter than 
with one of small diameter. The magnet is required to ex- 
ert a pressure of 3,000 pounds. Asisum'ing a pressure of 270 
pounds per square inch, the contact area will be 11.11 or 5.55 
on each side. The cross section of the magnetic circuit will 

14 
be 5.55 X — equals 7.77, 

10 

Assuming a cofl 1 inch by 2 inches, ais in Fig. 33b, 'the oiilt- 
side dJiameter of magnet will be 12 inches. The 'thicktiess 
of the wall -will be .2 inch to give an area 'of 7.77 squai^ 
inches in each side. The outside diameter of inner ring will 
be 9.6, and the inner wall will be .26 thick* 



264 



6. Area of magnetic circuit equails 2x2x.7854 equals 3.14. 
Assume 100 turns. on each coil: 33,000 lines musit flow per 
square inch. 

104,720x2x.3132 

A. t. equals equals 21,000. 

3.14 

Amperes in each coil equals 105. 

7. Annultir, as shown in Fig-. 33a. 

8. Sectional area of magnet equals 5.8 square inches, 
assuming a pull of 270 pounds per square inch. Thickness 
of outside wall is aibout 1-3 of an inch. Assume coil to be 
IVi inch deep. Length of magnetic circuil equals about Qy^ 
inohes. A. t. equals 6i/^x25 equals 487. Add 300 a. t. for 
constricted portion of the circuit, or a. t. equals 787. 



ANSWEES TO QUESTIONS ON CHAPTER VI. 



1. Mag-netic lines that are produced but do not pass 
thruug*h -that part of the circuit that they were intended to 
traverse. 

2. From 15 to 800 times better than air. 

3. By exposing" as little pole surface as possible to the 
air and having- rounded corners on w^hat is exposed. 

4. Because the surface at full magnetic difference of 
potential exposed to the air is so great in the Edison and 
so small in the internal pole. 

5. About 8,800 t<hrough eadh slot. 
G. About 64,000. 

7. Because iron conducts magnetic lines a few hundred 
times better than air and copper conducts electric current 
millions of times better than air. 

8. No; it only makes the magnet core and yoke heavier 
than they would otherwise be. 

9. Magnetic leakage is apt to draw nails, oil cans, 
wrenches, etc., into the poles, when they may be entangled 
with the armature. 

10. Small magnetic leakage and the removal of sur- 
faces that would attract iron pieces from much chance of 
drawing anything into the armature. 

11. The number of lines that pass tihrough the field 
magnet core divided by the number thjat pass through the 
armature. 

18 



ANSWERS TO QUESTIONS ON jOHAPTER VIT. 



1. 


See formulae Nos. (8), (9)iand (10) in text. 


2. 


746. 


3. 


6x500 equals 4000. 




61/2x746 


A 




**• 


- equals aniperes equajs oi,o-> 
110 


6. 


.0663. 


6. 


134. 


7. 


4.97 per cent. 


8. 


No. 




32 


9. 


— amperes. 
55 



10. On 110 volts 6.782, on 220 volts 3.391, on 500 volts 
1.492, on 1000 volts .746, on 10,000 volts .0746. 

11. On no volts 9.09, on 220 volts 4.545, on 500 volts 2, 
on 1,000 volts 3, on 10,000 volts .1. 

12. Because the voltage Is hig-her and the current lower 
than if the dynamos were in parallel. 

13. More economical because the voltage would be still 
further raised and the current reduced in the same ratio. 

14. Because dt permits of the use of a cheap line with 
only small loss of power. 



267 



15. It could not be aooomplislied with 250 voUts. 

16. It could noit 'be aooomplished with 500 watts. Abon^. 
95 per cent of the 100 horse power would be losit in the line 
at 1,000 volts; 49 volts or ISO waitts or 14 of 1 per cent, with 
20,000 volts. 

17. Because with the same copper cost the amount or 
weight used is the same, and if this is run two inches in- 
stead of one, the resistance of each mile is doubled and the 
miles of line are doubled, and therefore the resistance quad- 
rupled. 

18. As the square of the voltage. 

19. The distance varies directly as the voltage. 

20. 0000 wire is the nearest stankiard size, and this will 
cost $506.40. 

21. Three No. 000 wires can be used, and this 'will cost 
$1,140.75. 

22. The drop s-pecified in 'this question should have been 
omitted, and then the current would be 123.3. 

23. Because tihe armature generates voltage and when 
it is in operation there is no way of measuring what is used 
in the armature resistance. Therefore the other two for- 
mulae that contain the voltage lost cannot be easily applied. 



ANSWERS TO QUESTIONS ON CHAPTER VIIL 



1. To know the length of the average turn, 

2. See text. 

3. 4129. 

4. No. 17. 

5. 32,400. 

6. Because the number of a. t. is increased with the 
same size of wire if it is small in diameter, and a small wire 
and small power will therefore produce more a. t. if of 
small circumference than if of large. 

7. In order to have section enough of iron to allow the 
magnetic flux to pass. 

8. Because an increa.se in the amount ocf itlhe wire de- 
creases the current that flows through 'the coil in the same 
proportion tha^t it increases the turns. 

9. Yes. A heavy coil requires only a small amount of 
current to produce a given magnetizing power, an^ there- 
fore runs cooler. 

10. For 6-volt plafting dynamo No. 6 wir-e gives 2788c 
For 110-volt dynamo No. 18 givels 3150. 

For 220-volt dynamo No. 21 gives 3165. 
For 500-violt dynamo No. 24 gives 3612. 

11. For plating dynamo No. 6 wire req'uires 1214 poundis. 
For 110-volt dynamo No. 18 requires 16 pounds. 
For 220-volt dynamo No. 21 requires 16 poumds. 
For 500-vdlt dynamo No. 24 requires 20i/> pounds. 



269 

12. One watt per square inch. 

13. If thicker than this the heat from the inside layers 
of wire has difficulty in getting" away to the outside surface. 

14. .21 of 1 per cent, per degree F. 

15. Divide the number of amperes that a coil of one 
pound will pass by the number of amperes it is desired to 
have the finished coil pass, and the result is the desired 
weight. 

16. iSize of wire required ds No. 20. Wedght of wire re- 
quired is 14 pounds per coil. 

17. 20.9 x>ounds of Xo. 21 wire gives 3,600 a. t. at full 
pressure of 250 volts and a heat loss of l^ watt per sq. in. 

13. Divide number of ampere turns required by num- 
ber of amperes that wili flow, and the result is the number 
of turns. 

19. It decrease the current by increasing the resist- 
ance through the coil and so decreases the power lost in 
the coil. 

20. It increases the resistance and so increases tne 
power lost. 



a:n^swers to questions in chapter IX. 



1. 100,000,000. 

2. See text. 

3. It is a device by which direct current is obtained 
irom an armature in the wire of which the current is alter- 
nating. 

4. Because there must be two paths for the passage of 
the current through a direct current armature, and each 
path contains only half the amount of wire that is used on 
the whole armature. 

5. 120 volts. 1,500 revolutions. 

6. See text. 

7. 1,3S8,SS9. 

8. The best winding will be two parallel of .072 wire, 
and the resistance of the armature will be .0816 ohms. Di- 
mensions of arm'ature will be found in Fig. 29. 

9. If the motor is of the same size it will only be neces- 
sary to double the number of iturns on the -armature. 

10. Twice as many turns are required on a gramme 
ring armature as oai a drum armature. 

11. In the gramme ring method of winding, adjacent 
coils are at a small difference of potential, and ft is easy to 
repair a coil if one gets out of order. 

12. 223.2 square inches. 

13. The number of wires will be doubled, (the seictional 
mrea will be halved, thus quadTupling the resistance. 



ANSWERS TO QUESTIONS IN CHAPTER X. 

1. The electro-motive force produced in an electrical 
device which tends to reduce the current which the rprim'ary 
electro-motive force would tend to produce. 

2. No. 

3. Because the counter electro-motive force is very 
nearly equal to the primary elect-ro-motive force. 

4. By an application of formula (14). 

5. 925.8 revolutions per minute. 

6. 3,174,600. 

7. Because as the temperature of the fields rise the 
resistance rises and the ampere turns decrease, consequently 
the flux decreases and the speed increases in the same ratio 
as the flux decreases. 

8. The Patton street car was an example of this, in 
which a gas engine drove a dynamo which on light loads 
and down grades charged la storage 'battery, while on heavy 
loads and up ^grades it became a motor and absorbed power 
from the storage battery. 

9. The fact that the flux through the armature is con- 
stant and the voltage lost due to the resisance of the arma- 
ture is very small, even at heavy load. 

10. Because the voltage lost in a large armature is rela- 
tively less for the same heating than in a smaller armature. 

11. Because it decreases the counter electro-motive 
force by decreasing the effective flux through the armature. 



.272 

12. Volts lost in armature with one ampere equal .08 
volts. Volts lost in armature with 30 amperes equal 2.4 
volts. The drop in speed in per cent, will be 2.4 divided by 
79.92 equals 3 per cent^ 

13. Because the ampere, turns on the field coil of a 
series motor, and therefore the magnetic flux through the 
armature, depend upon the load on the armature. 

14. Because the flux through the field magnets tends 
to become constant after the iron becomes saturated. 

15. The magnetic flux across an air gap is strictly pro- 
portional to the ampere turns expended in the air gaip, and 
if the iron is unsaturated at the highest voltage, practically 
all the ampere turns will be expended in the air gap and the 
flux through the armature will be proportional to the volt- 
age, thus making the speed constant. 

16. In the same way that the speed of a series motor 
does, but not in the same degree. There will be an upper 
limit set to the speed on account of the flux produced by 
the shunt coil. 

17. The torque of an armature is proportionial to the 
product of the current and magnetic flux through it. "When 
the iron is unsaturated the flux through the armature will 
be doubled by doubling the current, and the double flux, 
acting on the double current, produces four times the torque. 

18. To the current passing through the armature. 

19. On a constant potential circuit with no load on the 
armature the increasing speed produces an increasing coun- 
ter electro-motive force, which reduces the current <tihrough 
the fields, thms reduoing the flux through the armature, 
•which thus tends to further increase the speed. The oon- 



273 



gtant speed is finally reached on laceount of the mechandcial 
power required to rotate the armature at such a hig-h rate 
of speed. On a constant current ciroiiit the counter elec- 
tro-motive force tends to become equal to the primary elec- 
tro-m'oitive force. 

20. In two ways: First, by redticing the ampere turns 
on the field by means of a centrifug*al device; <a.nd second, 
by decreasing- the effective flux throug^h the armature by 
ro'cking the brushes. 



ANSWERS TO QUESTIONS ON CHAPTE'R XL 

1. Molecular friction. 

2. An alternating current would set np changes in the 
direction of the magnetic flux, and therefore produce hj^s- 
leresis, while a direct current would not. 

3. Because at the same numiber of revolutions per min- 
ute there are twice as many reversals of magTietism in a 
four-pole motor armature is in a two-pole. 

4. The direction of the magnetism is reversed in the 
iron core of an armature in passing from a south pole to a 
north pole. 

5. Currents other ithan the main current set up in an 
armature due to its rotation, which produce wasteful heat. 

6. In the same direction that the currents flow in <the 
wires. 

7. To prevent eddy currents. 

8. To prevent eddy eunrents in the copper, which would 
Tdc formed in the large solid conductor. 

9. With a very short air gap there will be tufts of lines 
flowing from the pole pieces to the armature teeth, and 
therefore the flux of lines from a small given area of sur- 
face on the pole piece changes and so prod'uces currents in 
accordance with Lentz law. 

10. The permeability of steel pole pieces Is so much 
^eater than that of cast iron that it permits of this tufting 
to a much greater extent than cast iron. 



275 

11. The armature in Fig-. 35 is four-pole and there will 
be two currents in one direction across it and two currents 
in the opposite direction. The voltage of one of these cur- 
rents will be .48, or practically % of a volt; the resistance 
will be 1.6 of an ohm in the whole ipath of one of these cur- 
rents. The watts lost will be .143 of a watt. The power 
lost will be % of a watt. 

12. No. 

13. To more perfectly insulate the larmiature discs 
from each other than is possible by means of the oxide on 
the surface of each disc. 

14. The heating of the armature ohans this paper in- 
sulation, and so loosens the armature discs on the shaft 
between the end plates. 

15. As the square of the speed. 



ANSWERS TO QUESTIONS ON CHAPTER XIL 



1. The action of the armature as a maignet due to the 
current which it generates passing around it. 

2. On the amount O'f current delivered "by the armature. 

3. In a general way it is magnetized ait right amgles to 
the fields. 

4. Because this pole pi^-ce is of opposite polarity to the 
pole produced in the armature, w'hile the pole piece which 
the armature is <iipproaching' is of the same polarity as the 
armature, and there is consequently (attraction between the 
first two and repulsion between the last two. 

5. The movement of tne brushes gives a component of 
the armature reaction, which tends to increase or decrease 
the flux produced by the field coils. 

6. In order to stop the sparking the brushes must be 
rocked in such a direction that the armature reiaction has a 
component which opposes the flux produced by the field 
coils. 

7. They would have to be rocked backward, in a direc- 
tion opposite to that of rotation, and this would produce 
severe sparking. 

8. In constant current dynamos. 

9. By rocking the brushes into various positions which 
controls the effect of the armature reaction in reducing the 
flux produced by the field coils, and so controls the voltage 
produced hj the dynamo. 



277 



10. By reducing' the current tliroiig-h the field coils and 
so weakening the flux, and consequently the voltage ipcro- 
duced. This effect is greatly assisited by the effect of arma- 
ture reaction aaid by rocking the brushes. 

11. They should be set forward in the direction of rota- 
tion, whi<ch wiJl usually cause severe sparking. 

12. "N'ot more than half the ampere turns in the field 
coil. 

13. A gramme ring armature has twice as many turns 
as a drum armature, in order to produce the same voltage; 
therefore this form of armiature has a great armature reac- 
tion with a given current. Armature reaction is necessary 
in a constant current machine and should be avoided as 
much as possible in a constant potential machine. Another 
reason Is that it is easier to insulate successfully a gramme 
ring armature for the high voltaiges produx;ed in arc mar 
oLines than a drum armature. 

14. The field is made multi-polar. 

15. A four-pole machine would have half the ampere 
turns on each armature pole and the same number of am- 
pere turns in the air gap on each field pole if the same 
voltage is to be produced. Therefore the armature reaction 
will be decreased by half. 



ANSWERS TO QUESTIONS ON CHAPTER XIH. 

1. It is reversed. 

2. Half the total armature current, 

3. Chiefly bn the field in whicli the coil is moving at 
the time, also on the resistance of leads and brushes. 

4. To reduce the current in the short circuited coil to 0. 

5. If the short circuited coil carries one-half the total 
armature current at the moment it ceases to be short cir- 
cuited, perfect comimutation v^ill have 'been effected. 

G. To retard the change of current in the short cir- 
cuited coil and so to produce sparking. 

7. None. 

8. Because in a dynamo rocking the brushes forward 
brings the short circuited coil into a magnetic field, that 
tends to reverse the direction of current in the short cir- 
cuited coil from what it was before it was short circuited, 
while in a motor the reverse is true. 

9. No. 

10. The production of over one-half the total armature 
current in the short circuited coil in the same direction that 
current flows in it after the coil leaves the brush. 

11. Rock them a long distance forward. 

12. The resistance between brush and commutator. 



279 



13. It 'tends to cause the eurrent to pass from the 
brush to the commutaitor evenly all over the brush. 

J 4. Over-commutflition is only possible where current 
is flowing" in opposition to the main current in one of the 
leads. 

15. On account of their resistance they tend to make 
the currenit enter the commutator evenly over the whole 
surface of the bruish. 

16. The g*reater resistance of the carbon brush pro- 
duces more heat than the copper brush with a g^iven cur- 
rent. 

17. It will stop it enitirely. 

18. Becaoise its resistance is very much hig^her. 

19. It allows time for the voltag*e to overcome the self- 
induction of the coil to be coanmutated. 

20. See text. 

21. The arc that is formed between bar and brush 
m^^elts the edge of the copper bar and it appears as a fi-^e 
liake of copper dusit. 

22. It musrt; be very low in order to avoid sparking'. 

23. It elhows that the commuta'tion produced on ac- 
count of the resistance of the brush is of much more im- 
portance in perfect commutation than that produce^ by 
the ma.gnetic field. 



ANSWERS TO QUESTIONS IN CHAPTER XIV 



1. As a conductor in which E. M. F. is produced; sec- 
ond, as a conductor to carry the current to magnetize the 
fields. 

2. A circle surrounds the greatest area with the least 
length. 

3. It reduces the leakage surfax^es. 

4. It must all flow in the same direction. 

5. Because the N. and S. poles are 90 degrees apart. 

6. 36 degrees for 36 degrees is 1-10 of the circumfer- 
ence of a circle, and current must flow in opposite direc- 
tions in zones 36 degrees wide. 

7. In order that the mechanical force shall he exerted 
in all the wires under the two poles in the same directions 
as explained in chapter IV. 

8. 500 volts as a maximum. 

9. About 15.6 volts for both third and fourth and eley- 
enth and twelfth. 

10. The full voltage on the armature. 

11. One in which there is small difference of potential 
between coils in the same layer and the full difference of 
potential or voltage between the two layers. 

12. One in which each coil occupies the full depth of 
the vrlnding on the armature and in which there is a maxi- 
mum difference of potential between coils of the same layer. 



281 



13. 'By carryiiDg the leads or connection's from the ar- 
mature winding- spirally around the armature the desired 
distiance. 

14. A wave winding- is one in which it is possible to 
use two brushes on an armature for a four-pole naa chine 
without cross connecting- the commutator. Under the same 
circumstances a lap winding would require four brushes. 

15. Better magnetic balance in a uusymmetrical field 
and half the number of turns af wire. 

16. Because the magnet poles are 60 degrees apart. 

17. The positive brushes would be at degree, 120 de- 
grees and 240 degrees. The negative brushes would be at 
60 degrees, 180 degrees and 300 degrees. With a wave- 
wound armatu)re it is necessary to use only one positive and 
one negative brush, and these may be selected on opposite 
sides of the commutator if desired. 

18. 216. 

19. 108. 

20. The wave-wound armature will have four times the 
resistance. 

21. By cross connecting the commutator or connecting 
opposite bars on the commutator to each other. 

22. The wave-wound armature will operate just as if 
the armature was central. In the lap-wound airmature one 
of the circuits will produce a higher voltage than 
others, and therefore tends to produce loioal currents in 

the armature. 

23. It cannot be connected symmetrically tO' the com- 
nautator. 

19 



282 



24. Diagram, Fig*. 62. 

25. A djTiamo which has both series and shunt coils. 

26. To produce a machine which will produce a con- 
stant voltage on a variable load. 

27. The speed drops with increased load; volts lost in 
the armature drop, the armature reaction decreases the to- 
tal flux. These three causes decrease the voltage on the 
fields and therefore the ampere turns on the magnet. 

28. 4,200. 

29. A compound wound mofor has 'the chiairacteristics 
of both the series and shunt motors, the series winding 
making the speed variations greater than with the plain 
shunt motor. 

30. A compound wound motor will not spark on over- 
load and has a greater torque with the same current than 
a plain shunt wound motor. 

31. ■ At 500 volts the magnetic cirouit is nearly satu- 
rated, and the increase in the ampere tuTus due to fhe 
series coil does not produce a proportional inierease in the 
fiux, while at 250 volts it does. 



ANSWERS TO QUESTIONS ON CHAPTER XV. 

1. It causes self-excitation. 

2. No. 

3. Reversing the connections causes the current due 
to the residual magnetism to flow around the magnets in 
such a way as to decrease the residual magnetism instead 
of increase it. 

4. From two to five per cent. 

5. The saturation of the iron in the maorneTs. 

6. It would rise to an infinite voltage or until ^oxne 
part broke down. 

7. Connections between field and armature should be 
reversed. 

8. By bringing the machine up to speed, measuring 
the voltage due to residual magnetism with a mili volt me- 
ter, then making the connection with the field magnet coil 
and noting whether the voltage rises or falls when this con- 
nection is made. 

9. As the load begins to come on the voltage will fall 
very rapidly. 

10. Moving the rheostat arm increases or decreases the 
resistance in the shunt circuit. This changes the current 
through the shunt coil, which changes the ampere turns on 
the magnetizing circuit, and therefore the fiux and voltage. 

11. The arc obtained by suddenly opening a field cir- 
cuit. 



284 



12. 6,750 Tolts. 

13. 36,000. 

14. So that the circuit can never be entirely opened. 

is. In order that the possibility of a field discharge 
inay be avoided. 

16. The ends of the shun^t coil are always connected by 
the resistance in the starting box and the armature. 

17. To insert the resistance of the starting box in series 
with the armature to avoid sudden overload on the arma- 
ture when the current returns. 

18. With a series and shunt winding opposing each 
other. See text. 



ANSWERS TO QUESTIONS ON CHAPTER XVI. 



1. A break in the armature wili'dinig' which prevents the 
passage of the armature current. 

2. By severe arcing on the commutator. 

3. By connecting together the two commutator hars 
between which the arc occurs. 

4. A connection in the armature or commutator which 
allows a local current to flow. 

5. 2,750 amperes. 

6. By heating- the short circuited coil. 

7. It will completely short circuit the ""armature, and 
it will refuse to generate as a dynamo. 

8. It will run only a half revolution at a time. 

9. Imperfect contact between brushes and commutator. 

10. Continual contact and a constant pressure between 
brushes and commutator. 

11. See text. 

12. The inertia does not allow the brush to move 
quickly. 

13. Heating and cutting" the commutator and sparking. 

14. Forward in the direction of rotation. 

15. \Backward in the direction opposite to that of rota- 
tion. 

16. See text. 

17. An unintentional connection between the armature 
or field windinsr and the frame. 



286 

18. To sliort circuit part of the armature or field wind- 
ing. 

19. Yes. If it has only a single ground. 

20. To remove the intentional ground. 

21. By making tests and finding the point of lowest 
voltage between the armature winding and the core. 

22. If the short circuit is between the series coil and 
that part of the shunt coil connected to thTe pole of the 
machine opposite to that to which the series coil is con- 
nected, the machine will be completely short circuited. 

23. By refusing to build up if it is a dynamo and by 
refusing to carry a heavy load with an ordinary current if 
a motor. 

24. By short circuiting one coil after another and mak- 
ing a test each time until the field circuit as a whole is 
closed. 

25. To decrease its magnetizing power and cause it to 
run cooler. 

26. Because in the field c»oil the current is caused to 
flow by an external voltage, and if the resistance decreases 
the voltage decreases; while in the armature each turn 
produces a constant electro-motive force which is inde- 
pendent of the resistance of the circuit. 

27. By causing four times the amount of heat to oe 
generated in the field coil that remains in good condition. 

28. It causes a machine to act as if the field circuit was 
open, if there are only two field coils. 

29. By winding more wire on each field coil. 

30. The minute elongation of each tooth as it suddenly 
enters the magnetic field. 



ANSWERS TO QUESTIONS ON CHAPTER XVII. 



1. By the heat produced by the /passage of a current 
through the high resistance of a small carbon filament. 

2. Primarily to keep the filament from being burned up. 

3. Because it is absolutely necessary to preserve the 
vacuum, and platinum is the only metal that contracts and 
expands at the saane rate as glass. 

4. It must be constant. 

5. From 21/2 to 4%. 

6. If one is paying for both lamps and electricity and 
wan'ts light, it will pay to remove the dim lamps and replace 
them v\dth new^ ones at such a time the t the cost of current 
and lamps to produce a given amount of light shall be a 
minimum. 

7. About 7000 degrees Fahrenheit. 

8. Between 1-4 and 1-5. 

9. Because the light is more diffused. 

10. The oxygen of the air is excluded from the ho^ 
carbons. 

11. See text. 



A:>^SWEiT^S TO QUESTIONS ON CBDAPTBR XVni. 

1. A current proportional to the voltage. 

2. Ohm's law. 

3. Down through the plane of the paper, 

4. The eddy currents generated in the copper coil on 
n-h'ch the wire carrying* the current is wound. 

5. Magnetic field uniform. 

6. The mechanical force lacting on the w^ires carrying 
current and the reaction of the hair springs. 

7. On the constancy of the permanent magnet. 

8. A difference in the si^e of wire on the movable coil 
which in the ammeter is adapted to receive much larger cur- 
rents at a correspondingly lower voltag-e. 

9. See text. 

10. See text. 

11. The error introduced by the hysteresis of the soift 
iron. 

12. Write answer and compare with text. 

13. Write answer and compare with text. 



ANSWERS TO QUESTIONS ON CHAPTER XIX. 



1. A cnirent -which is cans tan tly reversing its direotion. 

2. From 12 to 16,000 per minute. 

3. The time required for two successive alternatioois. 

4. 36 2-3. 

5. By connecting a circuit to tv^o rings att|aohed to op- 
posite points on a direct current bi-polar commutator. 

6. The form of alteirnating current wave produced by 
a coil revolving in a uniform field. 

7. A single alternating current. 

8. Two alternating currents produced or used by the 
same machine in such relation to each other that when one 
is zero the other is maximum. 

9. To four- points 90 degrees apart. 

10. Three alternating currents having a certain rela- 
tion to each other set forth in answer to question 11. 

11. By taking current from three rings attached to 
three points on a two-pole direct current dynamo 120 de- 
grees apart, 

12. Because two-phase circuits are attached to points 
90 degrees apart on a direct current bi-polar commutlator, 
and to produce a three-phase to points 120 degrees apart. 

13. Fig. 86. 

14. The volts and amperes can be transformed by static 
apparatus. 



290 



15. A device of iron and copper by wliicli electric energy 
is transferred from one circuit o another without metallic 
contact. 

16. To receive a small current at a high, voltage and 
produce a large current at a correspondingly lower voJ't|age, 
or vice versa. 

17. On account of -the magnetic flux which is common 
to both the primary and the secondary coils. 

18. The self-induction of the coil produces a counter 
electro-motive force, which is very nearly equal to the pri- 
mary electro-motive force. 

19. The ampere turns' of the secondary coil oppose 
those of the primary, but the primary coil must always 
have enough ampere turns to force sufficient ma<gnetic flux 
around the circuit to keep up its counter eleotro-motive 
force. T\'hen the resistance in the secondary circuit de- 
creases, the current, by Ohm's law, increases, and the cur- 
rent in the primary must correspondingly increase. 

20. They are practically equal. 

21. A transformer of special design which has a small 
number of turns on the primary and a very great number 
on the secondary. 

22. On account of the flexibility of transformation and 
simplicity and reliability of generators andi motors. 



291 



ANSWERS TO QUESTIONS ON CHAPTER XX. 

1. Motors in other automobiles being piston-motors have 
a reciprocating motion which causes more or less vibrations. 

2. No such motor has been tried as yet; a steam — or gas 
■ — turbine would, however, have a rotative movement. 

3. The one larger motor used with single motor equip- 
ment is more efficient than each of the two smaller motors or 
the combination of the two motors used with double motor 
equipment. 

4. The use of two motors discards the differential gear, 
as each motor is geared to a driving wheel. This arrange- 
ment also facilitates the turning of corners, etc. 

5. See text. 

6. 1.6 H. P. See text and' Fig. 89. 

7. 113 R. P. ^I. See Fig. 89. 

8. 904 R. P. M 

9. 1st, speed position will give 5 miles per hour and 2nd 
speed position 10 miles per hour. 

10. Add water until hydrometer reads i.i. 

11. When fully charged the positive plates have a very 
dark, greyish brown color, and the negative plates a dark 
bluish or slate color. 

12. As discharge proceeds the color grows lighter. 

13. By application of ammonia, which combines with the 
sulphuric acid to form sulphate of ammonia, which is a harm- 
less salt. 

14. By adding to the electrolyte some carbonated soda. 
Sulphate of lead is to some extent soluble in solution of sul- 
phate of soda. Also see text. 



292 

TABLE XI. 
TENSILE 'STRENGTH OF COPPER VvTRE. 





Breaking weight 
Pounds 




Breaking weight 
Pounds 


SO 




SO 




1 »3 


Hard- 
drawn 


Annealed 


Hard- 
drawn 


Annealed 


0000 


8 310 


5 650 


9 


617 


349 


000 


6 580 


4 480 


10 


489 


277 


00 


5 226 


3 553 


11 


388 


219 





4 558 


2 818 


12 


307 


174 


1 


3 746 


2 234 


li 


244 


138 


2 


3 127 


1 772 


14 


193 


109 


3 


2 480 


1 405 


15 


153 


87 


4 


1967 


1 114 


16 


133 


69 


5 


1 559 


883 


17 


97 


55 


6 


1 237 


700 


18 


77 


43 


7 


980 


555 


19 


61 


34 


8 


778 


440 


20 


48 


27 



The strength of soft copper wire varies from 82 000 to 36 000 pounds 
per square inch, and of hard copper wire from 45 000 to 68 000 pounds per 
square inch, according to the degree of hardness. 

The above table is calculated for 84 000 pounds for soft wire and 
60 000 pounds for hard wire, except for some of the larger sizes, where 
the breaking weight per square inch is taken at 50 000 pounds for 
000,000 and 00,55 000 for 0, and 57 000 pounds for 1. 



TABLE Xll. 

CIRCUMFERENCES OF CIRCLES. 
ADVANCING BY TENTHS. 



Diam. 


.0 


.1 


2 


.3 


.4 


.5 


1 
.6 


.7 


.8 


.9 


Diam. 





.00 


.31 


.62 


.94 


1.25 


1.57 


1.88 


2.19 


2.51 


2.82 





1 


3.14 


3.45 


3.77 


4.08 


4.39 


4.71 


5.02 


5.34 


5.65 


5.61 


1 


2 


6.28 


6.59 


6.91 


7.22 


7.53 


7.85 


8.16 


8.48 


8.79 


9.11 


2 


3 


9.42 


9.74 


10.05 


10.36 


10.68 


10.99 


11.30 


11.62 


11.93 


12.25 


3 


4 


12.56 


12.88 


13.19 


13.50 


13.82 


14.13 


14.45 


14.76 


15.08 


15.39 


4 


5 


15.70 


16.02 


16.33 


16.65 


16.96 


17.27 


17.59 


17.90 


18.22 


18.53 


5 


6 


18.84 


19.16 


19.47 


19.79 


20.10 


20.42 


20.73 


21.04 


21.36 


21.67 


6 


7 


21.99 


22.30 


22.61 


22.93 


23.24 


23.56 


23.87 


24.19 


24 50 


24.81 


7 


8 


25.13 


25.44 


25.76 


26.07 


26.38 


26.70 


27.01 


27.33 


27.64 


27.96 


8 


9 


28.27 


28.58 


28.90 


29.21 


29.53 


29.84 


30.15 


30.47 


30.78 


31.10 


9 


10 


31.41 


31.73 


32.04 


32.35 


32.67 


32.98 


33.30 


33.61 


33.92 


34.24 


10 


11 


34.55 


34.87 


35.18 


35.50 


35.81 


36.12 


36.44 


36.75 


37.07 


37.38 


11 


12 


37.69 


38.01 


38.32 


38.64 


38.95 


39.27 


39.58 


39.89 


40.21 


40.52 


12 


13 


40.84 


41.15 


41.46 


41.78 


42.09 


4241 


42.72 


43.03 


43.35 


43.66 


13 


14 


43.98 


44.29 


44.61 


44.92 


45.23 


45.55 


45.86 


46.18 


46.49 


46.80 


14 


15 


47.12 


47.43 


47.75 


48.06 


48.38 


48.69 


49.00 


49.32 


49.63 


49.95 


15 


16 


50.26 


50.57 


50.89 


51.20 


51.52 


51.83 


52.15 


52.46 


52.78 


53.09 


16 


17 


53.40 


53.72 


54.03 


54.35 


54.65 


54.97 


55.29 


55.60 


55.92 


56.23 


17 


18 


56.54 


56.86 


57.17 


57.49 


57.80 


58.11 


58 43 


58.74 


59.06 


59.37 


18 


19 


59.69 


60.00 


60.31 


60.63 


60.94 


61.26 


61.57 


61.88 


62.20 


62.51 


19 


20 


62.83 


63.14 


63.46 


63.77 


64.08 


64.40 


64.71 


65.03 


65.34 


65 65 


20 


21 


65.97 


66.28 


66.60 


66.91 


67.22 


67.54 


67.85 


68.17 


68.48 


68.80 


21 


22 


69.11 


69.42 


69.74 


70.05 


70.37 


70.66 


71.00 


71.31 


71.62 


71.94 


22 


23 


72.25 


72.57 


72.88 


73.19 


73.51 


73.82 


74.14 


74.45 


74.76 


75.08 


23 


24 


75.39 


75.71 


76.02 


76.34 


76.65 


76.96 


77.28 


77.59 


77.91 


78.22 


24 


25 


78.54 


78.85 


79.16 


79.48 


79.79 


80.11 


80.42 


80.73 


81.05 


81.36 


25 


26 


81.68 


81.99 


82.30 


82.62 


82.93 


83.25 


83.56 


83.88 


84.19 


84.50 


26 


27 


84.82 


85.13 


85.45 


85.76 


86.07 


86.39 


86.70 


87.02 


87.33 


87.65 


27 


28 


87.96 


88.27 


88.59 


88.90 


89.22 


89.53 


89.84 


90.16 


90.47 


90.79 


28 


29 


91.10 


91.42 


91.73 


92.04 


92.36 


92.67 


92.99 


93.30 


93.61 


93.93 


29 


30 


94.24 


94.56 


94.87 


95.19 


95.50 


95.81 


96.13 


96.44 


96.76 


97.07 


30 


31 


97.38 


97.70 


98.01 


98.33 


98 64 


98.96 


99.27 


99.58 


99.90 


100.2 


31 


32 


100.5 


100.8 


101.1 


101.4 


101.7 


102.1 


102.4 


102.7 


103.0 


103.3 


32 


33 


103.6 


103.9 


104.3 


104.6 


104.9 


105.2 


105.5 


105.8 


106.1 


106.5 


33 


34 


106.8 


107.1 


107.4 


107.7 


108.0 


108.3 


108.6 


109.0 


109.3 


109.6 


34 


35 


109.9 


110.2 


110.5 


110.8 


111.2 


111.5 


111.8 


112.1 


112.4 


112.7 


35 


36 


113.0 


113.4 


113.7 


114.0 


114.3 


114.6 


114.9 


115.2 


115.6 


115.9 


36 


37 


116.2 


116.5 


116.8 


117.1 


117.4 


117.8 


118.1 


118.4 


118.7 


119.0 


37 


38 


119.3 


119.6 


120.0 


120.3 


120.6 


120.9 


121.2 


121.5 


121.8 


122.2 


38 


39 


122.5 


122.8 


123.1 


123.4 


123.7 


124.0 


124.4 


124.7 


125.0 


125.3 


39 


40 


125.6 


125.9 


126.2 


126.6 


126.9 


127.2 


127.5 


127.8 


128.1 


128.4 


40 


41 


128.8 


129.1 


129.4 


129.7 


130.0 


130.3 


130.6 


131.0 


131.3 


131.6 


41 


42 


131.9 


132.2 


132.5 


132.8 


133.2 


133.5 


133 8 


134.1 


134.4 


134.7 


42 


43 


135.0 


135.4 


135.7 


136.0 


136.8 


136.6 


136.9 


137.2 


137.6 


137.9 


43 


44 


138.2 


138.5 


138.8 


139.1 


139.4 


139.8 


140.1 


140.4 


140.7 


141.0 


44 


45 


141.3 


141.6 


142.0 


142.3 


142.6 


142.9 


143.2 


143.5 


143.9 


144.2 


45 


46 


144.5 


144.8 


145.1 


145.4 


145.7 


146.0 


146.3 


146.7 


147.0 


147.3 


46 


47 


147.6 


147.9 


148.3 


148.6 


148.9 


149.2 


149.5 


149.8 


150.1 


150.4 


47 


48 


150.7 


151.1 


151.4 


151.7 


152.0 


152.3 


152.6 


152 9 


153.3 


153.6 


48 


49 


153.9 


154.2 


154.5 


154.8 


155.1 


155.5 


155.8 


156.1 


156.4 


156.7 


49 


f50 


157.0 


157.3 


157.7 


158.0 


158.3 


158.6 


158.9 


159.2 


)59.5 


159.9 


50 



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i-IC0t-(»O-^ 



;^CO 



COCO'*-^"^ 



QO CO CO CO irt Oa 



t-OQOSCO 

■>*C<IOQOOO 
C<1 OS CO CO T-I 

c<i lira irt o T-i 



' CO o OS OS 1 
T-ioa cvicoi 



OiOc<j»rt OS 

CDOSOO-^C- 

t-^ p c-^ 1-i p 

CO* '«* ^* ^ oi 
OSthcc ior- 



coosc^co c~ 

OC<J irt OOi-t 
CQ C<1 C<J C<l CO 



t^t- t-ooos 

CO OS OS coo 

p Irt P T-1 OC 

Os' CO* OS* CO* ■^* 
■^oOth »ft OS 

COCQ'*'^'^ 



oot-cQOs 



•<*<COCO-*Q 



SS gSsgSS^ 



COt-C<IQO»« 
CO® coco iH 
OOt'Osc- 






•iHCO-<*C0-^ 
OC<IiOOQt-I 

c<i c<i c^J c3 CO 



i-icoco( 

CO CO t- < 

CO T-I '^( 



CO-^ COOi«COO 

c3co CO CO "^ -<t< x* 



5DC-0QOSQ y^O^eQ-^fa COfOOgjO t^C^ICC-^iO «OC-»CyOSQ 
C<JC<l^(MCO eOCCCOCOCQ COOQrtJS'^ ^"^"^"^"^ "i**"^ «<"^IS 



m 



Eh 

o 

I— I 

o 
< 



cs3?Dt-»oQ «03oos<ico Oiftt-eoM ift»r:c<it-oo t-09i«iftca 

cocooii^^c^ c<iTHir5?oN "TiH^TH"<*cooq oq-^^^oco?© »«oo«ooo 

QOi-<»AN'oi 050c<3coc^* osodococo odioccco-^* t-'wodirt'^ 

^S^irtO-^ OSLiOir:^ cDMoOirtTH t-'«*'i-Hoo»rt c^jgc^irtco 

»0«0«OC^tr- t-oOOSOsO Oi-if-tCVlCQ CO -^ »rt irt ?0 t-oooOOiQ 

tH tHt^t^i-1tH i-H iH tH t-( tH iH r-l rH Tt ^ 

OOC*?©?© C<I<£)t-»rtO C<lT-tC-00 00 03 "!*< C<J CX) i^i-iOQCOOO 

i-joi""!!;-^© (M^ 05 c<i i-H «> <:dc<ic»5i-j'<i< c<i t-^ c-^ CO "^^ cjiflcooqco 

"^'cDTHt-^ift "(j"* ■^' c^' i-J o ccri^i-^*c-^ oioQ^'^o^- Q-^'ot-'«0 

COQiOOS"^ Oi"^aii«Q CD^aX)-^Q t;?0Ot-'»*< ?J05C"^M 

iOC0?0'X)t- t'ooaocso o»-<ti(m52 00 -^ urs »r: iX) t-c-ooasO 

1-1 Tl T^ •rt TH T-l lHT-(TlTHl-t r1 T-^ TH T-1 OJ 

coas«ocoiH ooos<i _ 

Or^C<105C0 •«!*< Cv] C- Oi 30 •^OOOOCOQ C^Ji-lt^OiQ t^T-(C<JQ<© 

C5 O 05 !>; C<1 C^] 00 05 CD 05 00 C^^ Kl 00 O C-^ O 00 (^J « 00 O C-^ O OO 

oi C^' <X> C<1 O 05 05 ^ iC Q C-^ to ?0 t-* 1-1 irt cm' 05 05 O (M* t-^ oi O 00 

irtO'^Oi-^ OOr^O-^Q iOtHC-COQ <£)?0C5«D'^ t-i 00 ?D ■>* i-( 

L^CO^OOC- t»0000050 Oi-ItHC<ICO OO-^-^lCCO C^C^OOOiO 

t-^OiftcOt- OO— ^iftCi-^ 

1-t 00 03 CO ■■-( COOiOO-'tiOO OiCDi-iC0C<l 00 tH •!-( 00 C<1 "TfOigOOQ 

c-s<i'<*T-j-<i^^ c^icococvirs ococ^oito i-jcooc^i^^ m irt p n os 

icoo'c^iodio ■>*'-«*' cc o lo oioo-pH-^' os i« co' (M* co* i«aiioc<j'o 

irtos-^ooco oocooQ-^os iftiHc-coos ift c<i a: CO CO oc^iocoi-i 

irSiOcocDt- t^ooocosoi Oi-hi-kmc^ cO'^'<*»aco t-t^oooio 

t-(i-IiHtHtH l-H T-li-l 1-1 iH l-HT-n-(iHCq 

t-OOi-H-^OO C000lOC<IQ 

"**»C'>*05'^ thc-t-iC^O ■^COiflC^Jifl irtNC^OOlr- C0i^»OC<l«O 

»rt C5 OS -^^ «0 CO »rt -^^ OC X) CO "^^ -i-j "^^ C<l ?0 CO TH OCl C5 C<1 O -^ -^^ 05 

1-H rf t-* cf Q* Ci OS •-I -.jf. OS Co' '^' -<* KTS od C<I* 0» CO krt Ift o6 C<I t-* ■^* C<l* 

»«C5CC0QCO t-C<IOOCOOO ^OOOdOO »ftTHOOirtC<] OSC--*tiC<IQ 

»r5i«cocot- c-oooo050i O th T—( c^ 5^q co-^-^irseo coi^-ooosp 

NCOCQOOkO C^ItHQOi-* 

OS'-rC-COCO t-OOCDi-»CO C<I OO tH C<1 Oi "^ CO -<*^ Q CO CO Q ^ tO -^ 

coco-'^oqoq co --^^ i-j "«* oa ?o»rti-jcv3oq i-hoscccooo osSobeop 

t-' OS CO oo' »« -"i- '^* CO* OS -^ o 00 00* OS 1-H cb i-I os* oo' oo' Q* -<* os* co id 

•«<* OO CO C— C<I C— COC— CaoO ^9*OSI«i-H0Q "»*i i-Hlr- ■** iH ^COCOt-IOS 

iftirtCOCOC- C-0000O5O5 OOthc<1c5. CO ««* "«t iTt CO CO C^ 00 OS OS 

CO O OS 00 t^ oo OS CO tH OS 

iO»Ai-tirtCO -<*OSC<]i-(i:- T-(THgS"**<CO '«#OC0C0iH »ftCO»«QCO 

C<1 CO p C^3 O "<* CO OS O p OS C'^ p p l« p CO »fi CO tr-^ p T-1 CO^ p iH 

coiftos'-'*'^ OS OS* O'*' 00 -^ c<i c<i* CO o OS »o c<i 1-i iH cot^c<io6t^ 

•^OOCMt-C^l CO T-i C- 03 t- C0OSiOi-Ht»- CCOC'-^i-l OOiOCOOOO 

jrsincocot- c^ooooosos ooi-hc<ic<j co'^-^irtco cot-ooosoi 

OSOt— ICOCO 0S-^05iftC<l 

oac-oocoi-t cococsco'sn ^<ooot-co cot--«*gQO ^-"^c^c-oo 

•?-i o ir:;^ CO CO in co co p th c<j oq p oo w r-j p c^ co p co t-; ?o th n 

os'i-J-*oscd -.**-.* ift 30 CO OS* CO CO CO OS coooia-^'* toai-^-^ai 

COOOC<ICOtH CO'^CO--hc^ C<100"«*iOCO CO^COCOO C-'«*C<IQ^- 

u^irtcocot' t-ooooosos ooTHPJoa coco-^inco cot-ooOTOs 

C<JirtOS-^0 CO-^C<JOO 

MOiftOOQO "^OOOSC-C^J ■^COOSNCO 0»OCO»«tH COCOOiCCQ 

pOOT-jpiO pC<l'<tC<lp loppc-;p t-;PP"^U5 rH CO t-J "^^ CO 

iftco'OkftTH os^ocot- cOi-JoQc^i «Doao6c^t^ osc<ic^coi-J 

COC-C^ICOtH IOOCOtHCO O^OO-^OCO C<10S»OC<IOS CO'^tHOSC* 

»OiaCDCOC-» C-O000O5O5 O O rH eg CO CO CO "^ lO ift CO t» 00 00 Oi 

OCOCOtHO OSOSOCOift 

COirtiOCOCO CO'^OCOtH t-T-(iHOS'<* irt't^OCOCO Q"^«0'^0 

piot-jfloq tr-^coppiH oqc<iTH»«p co'^^coio-^ij cBp»r;c-^io 

QCOiOQCO* "<iJ -^* m* C-* C<i t-* i« •^* •^* CO QwriCOOQ* 1-i ■^' OS* ift* CO 

COc-i-H®0 iftQirsOCO 2^C;-C0OS»« 55 OO iO CO OS COCCOOQCO 

iciftcocot- t-ooooosos oOt- — CO co'-o-^inifl coc-oooooa 



3 



ssisss snn^^ ississs ssssss sssss 



9M 



TABLE XIV. 



AREAS OF SMAIiL CIRCLES. 



ADVANCING BY HUNDREDTHS. 



s 


.00 


.01 


.02 


.03 


.04 


.05 
.00196 


.06 


.07 


.08 


.09 


,0 


.0 


.000078 


.00031 


.0007 


.00125 


.00283 


.00385 


.00503 


.00636 


.1 


.0078 


.0095 


.00113 


.0133 


.0154 


.0177 


.0201 


.0227 


.0255 


.0283 


.z 


.0314 


.03464 


.038 


.0415 


.0452 


.0491 


.0531 


.0572 


.0616 


.0666 


.3 


.0706 


.0755 


.0804 


.0855 


.0908 


.0962 


.1018 


.1075 


.1134 


.1195 


A 


.1256 


.132 


.1385 


.1442 


.1520 


.1590 


.1662 


.1735 


.181 


.1886 


.5 


.1963 


.2043 


.2124 


.2206 


.2290 


.2376 


.2463 


.2552 


.2642 


.2734 


.6 


.2827 


.2922 


.3014 


.3117 


.3217 


.3318 


.3421 


.3526 


.3632 


.3739 


.7 


.3848 


.3959 


.4071 


.4185 


.4301 


.4418 


.4536 


.4657 


.4778 


.4902 


.8 


.5026 


.5153 


.5281 


.5411 


.5542 


.5674 


.5809 


.5945 


.6082 


.6221 


.9 


.6362 


.6504 


.6648 


.6793 


.694 


.7088 


.7238 


.739 


.7543 


.7698 



TABLE XV. 



PRICE LIST OF COPPER MAGXET WIRE. 



Size, 
B. &S. 

Gauge 


Cotton 


snk 


Single 


Double 


Single 


Double 


16 






$ 1 12 


$ 1 53 


17 






1 12 


1 53 


18 






1 15 


1 57 


19 






1 15 


1 57 


20 


$ 060 


$ 74 


1 18 


1 61 


21 


70 


88 


1 20 


1 63 


22 


76 


95 


1 30 


1 76 


23 


83 


1 05 


1 42 


1 93 


24 


90 


1 14 


1 56 


2 13 


25 


100 


1 27 


1 81 


2 4& 


26 


1 10 


1 38 


2 10 


28» 


27 


1 25 


1 57 


2 25 


3 07 


28 


1 35 


1 69 


238 


3 27 


29 


1 50 


1 89 


2 75 


3 76 


30 


1 65 


2 07 


2 95 


4 02 


31 


1 80 


2 23 


3 25 


440 


32 


1 95 


2 28 


345 


4 53 


33 


2 40 


2 85 


390 


5 10 


34 


2 85 


3 42 


4 10 


5 30 


35 


3 25 


388 


5 85 


7 78 


36 


4 37 


4 93 


7 00 


888 


37 


6 75 


7 25 


11 00 


13 63 


38 


900 


9 50 


13 00 


14 50 


39 


1100 


12 00 


15 00 


18 00 


40 


13 00 


15 00 


20 00 


23 00 



298 



TABLE XVI, 



SPECIFIC GRAVITIES OF METALS. 



Names of metals 



: vaiminiim, cast 

hammered 

Antimony , 

Arsenic 

Barium 

Bismuth 

Cadmium 

Calcium , 

Chromium 

Cobalt 

Copper 

** rolled 

*' cast 

*' drawn 

" hammered 

** pressed 

" electrolytic 

Gold 

Iron, bar 

** wrought 

Steel 

Lead 

Magnesium 

Manganese 

Mercury 

Nickel 

Platinum 

Potassium 

Silver 

Sodium 

Strontium , 

Tin 

Zinc 



Specific 
gravity 



2.5 
2 67 
6.702 
5.763 
4. 

9.822 
8.604 
1.566 
73 

8.6 

8.895 
8.878 
8.788 
8.946 
8.958 

8.931 
8.914 
19.258 
7.483 
7.79 

7.85 
11.445 

2.24 

6.9 
13.568 

7.832 
20.3 

.855 
10.522 

.972 

2.504 
7.291 
6.861 



Weights 

per cubic 

foot 



156 06 
166 67 
418,37 
359.76 
249.7 

613.14 

537.1 
97.76 
455.7 
536.86 

555.27 
554.21 
548.59 
558.47 
559.25 

557.52 
556.46 
202.18 

467.18 
486.29 

490.03 
714.45 
139.83 
430.73 
846.98 

488.91 
267.22 

54. 
656.84 

60.68 

156.31 
455.14 
428.29 



Specific 
heat 



.214 3 

056 8 
.081 4 



.030 8 
.056 7 



.107 
.095 1 



.032 4 

.13 

.113 

.116 

.asi 4 

.249 9 
.114 
.031 9 

.109 1 
.032 4 
.169 6 
.057 
.293 4 



.056 2 
.095 5 



Melting 
point in 
degrees 
Fahr- 
enheit 



810. 
365. 



497. 
500. 



1 996. 



016. 

786. 
286. 

286. 
612. 



3 000. 



280 0. 
328 6. 

136. 
1 873. 

194. 



442. 
77SL 



WIRE GAUGES IN MILLS. 
TABLE XVII. 







Brown 


Birmingham 




Numbers 


Roebling 


& 


or 


New British 






Sharpe 


Stubs 


standard 


000 000 


460. 






464. 


00 000 


4:^. 


. 




432. 


0000 


393. 


460 


454;* 


400. 


000 


362. 


409.6 


425. 


372. 


00 


331. 


364.8 


380. 


348, 





307. 


324.9 


340. 


324. 


1 


283. 


289 3 


300. 


300. 


2 


263. 


257.6 


284. 


276. 


3 


244. 


229.4 


259. 


252. 


4 


225. 


204.3 


238. 


232. 


5 


207. 


181.9 


220. ^ 


212. 


6 


192. 


162. 


203. 


192. 


7 


177. 


144.3 


180. 


176. 


8 


162. 


128.5 


165. 


160. 


9 


148. 


114.4 


148. 


144. 


10 


135. 


101.9 


134. 


128. 


11 


120. 


90.74 


120. 


116. 


12 


105. 


80.81 


109. 


104. 


13 


92. 


71.96 


95. 


92. 


14 


80. 


64.08 


83. 


80. 


15 


72. 


57.07 


72. 


72. 


16 


63. 


50 82 


65. 


64. 


17 


54. 


45 26 


58. 


56. 


18 


47. 


40.3 


49. 


48. 


19 


4L 


35.89 


42. 


40. 


20 


35. 


31.96 


35. 


36. 


21 


32. 


28.46 


32. 


32. 


22 


28. 


25.35 


28. 


28. 


23 


25. 


22.57 


25. 


24. 


24 


23. 


20.1 


22. 


22. 


25 


20. 


17.9 


20. 


20. 


26 


18. 


15.94 


18. 


18. 


27 


17. 


14.2 


16. 


16.4 


28 


16. 


12.64 


u. 


14.8 


29 


15. 


11.26 


13. 


13.6 


30 


14. 


10.03 


12. 


12.4 


31 


13.5 


8.93 


10. 


11.6 


32 


13. 


7.95 


9. 


10.8 


33 


11. 


7.08 


8. 


10. 


34 


10. 


6.3 


7. 


9.2 


35 


9.5 


5.62 


5. 


8.4 


36 


9. 


5. 


4. 


7.6 



300 



TABLE XVIII 



DECIMAL EQUIVALENTS OF PARTS OF AN INCH. 



8tll8 


leths 


32ds 


64tlis 


14 equals .125 
}4 " .250 
% " .375 
Yi ♦* .500 
% - .625 
% " .750 
% *' .875 


^ equals .0625 
T^ " .1875 
^ " .3125 
^ " .4375 
j% " .5625 
ii " .6875 
if " .8125 
M " .9385 


g^j equals .03125 
3^2 " .09375 
3^2 *' .15625 
/2 " .21875 
5% " .28125 
H ** .34375 
H * .40625 
if " .46875 
ii . " .53125 
M " .59375 
§^ " .65625 
§i *' .71875 
M " .78125 
§5 *♦ .84375 
H " .90625 
M ** .96875 


^ equals .015625 
^\ " .046875 
B-k " .078125 
^\ " .109375 
^\ " .140625 
H ** .171875 
if ** .203125 
M " .234375 




U " .265625 






if " .296875 






ii *' .328125 






II " .359375 






If '* .390625 






U " .421875 






if " .453125 






U " .484375 






il " .515625 








II " .546875 








U " .578125 








if " .609375 








ii " .640625 








■*i " .671875 








if " .703125 








H " .734375 








11 " .765625 








li " .796875 








If " .828125 








II ** .859375 








II " .890625 








II " .921875 








IJ " .953125 
If ♦* .984375 

















ja 




«o 


Ob 


(M 


^i^ 


t^ CO 
















"~ 


h- o 


•-H 


CO 




'^ 




00 


00 


OS 


p^ 










<N r- 


g 


^ 


^ 


S 


^ cs !^ 


g 


CO 




g 


CO 


-^ » 00 «o 

00 Tt< ^ o o 

'^. '*. I^ ^. t=^ 




s 


i.%%^. 


si 


q o o 




5 

o 


o 




s 


























f-I fi 


(1.° 


O 




















































< 


si 


00 o 


o 


■*J< 


•1? 

CO 


?l 


2g?3 


C<1 


CO 


00 


00 


o 


00 CO 00 ri (M 

O -^ OS 00 I-I 

q "^. <^^ '^ q 


^^ 


Si 


'4 


§ 


c§ 


CO* <M* CO* 




o* 


s 


f§ 


o 


O t>I OS* rH CO 

r»- r- OS CO OS 

"^ CO (?^ c^ r-; 


O 

z 

< 




g^ 


t>» 


s 


CO 


^ 


ISS 




^ 


OS 


^ 


"^ 


OJ 


'N O 


iO 


lO 


o 


t->. 
















w.":: 


r^ Tj* 


■^ 


i-H 


lO 


CO 


t^ Lt) t^ 


<M 


lO 


•o 


t-. 


1 


lllll 


C/3 


li 


CO -"^ 


i 




i 


CO 
CO 


»-: ". ^-. 




00 


1 


§ 


« 








1— J 


1—1 


rH CS C^ 


CO' 


Tf 


iO 


CO* 


00* 


1-H* CO* t>r CO* i> 


a 
























^ 1-H ,-H CO CO 


. 


t^ o 


<-H 


iC 


(M 


r^ 


c^ 00 CO 


o 


00 


CO 


•o 


l>. 






wC^ 


•^ ^ 


o 


00 


l- 


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t- ^ CO 




1— ( 


o 


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CO b- CO o t>. 

1-^ OS ^-1 00 v^ 




Ti 23 


o 


CO 


CO 


o 


00 "^ C<l 


OS 


^M 






CO 




cM 


00 o 


CO 


CO 


o 


CO 


(>i rj <N 


O 


CO 


CO 


?^ 


CO 


O rt< ^ r-l OS 

-i CO CO CO i-i 




O r^ 


•^ 


'^ 


<N 


«i 


CO "*, iC 


-q, 


00 


q 


2 


q 




o2 


















" 




i-i 


CO CO* CO r5^* to* 


X 


"2 


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o 


t^ 


00 


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CO ^ CO 


OS 


t^ 


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CO 






H 
C 
2 


oo CO 


Tt^ 


OS 


o 


c^ 


^ 00 rt< 


00 


oo 


-^ 


CO 


00 


^. o ^ l^ S5 


O O 


r-i lO 


C<l 


CO 


1— 1 


lO 


00 C^ '^ 


t^ 


CO 


"* 


°9 


CO 


«o «o 


00* 


o* 


CO* 


CO* 


S S 22 


«— 1 


CO* 


CO 


CO* 


!2 


CO 00* ^ t-^ CO* 








t— « 


r-i 




(M r^ CO 


"^ 


lO 


CO 


00 


o 

r-i 


CO CO — CO CO 
--« r^ CO CO CO 




z 

< 


s. 


























mii 


























X 

o 


ci 


^ ^ 


^ 


^ 


^ 


•«*< 


00 o o 


lO 


^^ 


CO 


OS 


,_,' 


CO CO 'cO CO t>- 


3 ^ 


CO lO 


CO 


00 


«. 


-^ 


C<l OS CO 


CO 


CO 


Tt< 


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TABLE XX. 
AREAS OF DIFFERENT WIRE GAUGES. 



X 


B & S GAUGE 


B. W. GAUGE 


i 

2 


Diam. 
Mils. 


Circular 
Mils. (d2) 
1 mil.= 
.001 inch 


Diam. 

Mils. 


Circular 
Mils. {d2) 
1 mil.= 
.001 inch 


000 

000 

00 


460. 

409.6 

364.8 


211 600. 
168 100. 
133 225. 


454. 
425. 
380. 


206 116. 
180 6-25. 
144 400. 




1 

2 
3 
4 


324.9 
289.3 
267.6 
229.4 
204.3 


105 625. 
83 521. 
66 564. 
52 441. 
41 616. 


340. 
300. 
284. 
259. 
238. 


115 600. 
90 OCO. 
80 656. 
67 081. 
56 644. 


5 
6 
7 

8 
9 ■ 


181.9 

162. 

144.3 

128.5 

114.4 


33 124. 
26 244. 
20 736. 
16 384. 
12 996. 


220. 
203. 
180. 
165. 
148. 


48 400: 
41 209. 
32 400. 
27 225. 
21 904. 


10 
11 
12 
13 
14 


101.9 
90.74 
80.81 
71.96 
64.08 


10 404. 
8 281. 
6 561. 
5 184. 
4 096. 


134. 
120. 
109. 

95. 

83. 


17 956. 
14 400. 
11 881. 

9 025. 

6 889. 


15 
16 
17 

18 
19 


57.07 

50.82 

45.26 

40.3 

35.89 


3 249. 
2 601. 
2 025. 
1 600. 
1 296. 


72. 
^. 
58. 
49. 
42. 


5 184. 
4 2>5. 
3 3^4. 
2 401. 
1 764. 


20 
21 
22 
23 
24 


31.96 
28.46 
25.35 
22.57 
20.1 


1024. 
812.3 
&40.1 
510.8 
404. 


. 35. 
32. 
28. 
25. 
22. 


1 225. 
1 024. 

784. 

625. 

484. 


25 
26 
27 
28 
29 


17.9 

15.94 

14.2 

12-64 

11-26 


320.4 
252.8 
201.6 

158.8 
127.7 


20. 
18. 
16. 
14. 
13. 


400. 
324. 
256. 
196. 
169. 


30 
31 
32 
33 

34 


10.03 
8.93 
7.95 
7.08 
6.3 


100. 
79.2 
64. 
50.4 
39.7 


12. 

10. 

9. 

8. 

7. 


144. 
100. 

81. 

64. 

49. 


So 
36 


5.62 \ 31.4 
5. 25. 


5. 


25. 
16. 



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ELECTRICAL WOEDS, TERMS AND PHRASES DEFINED 



A. C. — Abbreviation for alternating" current. 

ACCELERATION— The rate of change of speed or velCKjity. 

ACCUMULATOR, A SECONDARY OR STORAGE CELL— 
Two inert plates partially surrounded by a fluid inca- 
pable of acting chemically on either of them until after 
the passage of an electric current, when they become 
capable of furnishing an independent electric current. 

AFFINITY, CHEMICAL— Atomic attraction. 

The force which causes atoms to unite and form chem- 
ical molecules. 

ALARM, BURGLAR — A device, generally electric, for auto- 
matically announcing the opening of a door, window, 
closet, drawer, or safe, or the passage of a person 
through a hallway, or on a stairway. 

ALARM, ELECTRIC— An automatic device by which atten- 
tion is called to the occurrence of certain events. 

ALLOY — A combination, or mixture, of two or more metal- 
lic substances. 

ALLOY, GEEMAN SILVER— An alloy employed for the 
v-zires of resistance coils, consisting of 50 parts of cop- 
per, 25 of zinc, and 25 of nickel. 



AMP ^06 

ALPHABET, TELEGRAPHIC: MOESE'S— Various group- 
ings of dots and dashes, which represent the letters of 
the alphabet or other signs. 

ALTEKXATIONS— Changes in the direction of a current in 
a circuit. 

A current that changes its direction 300 times per sec- 
ond is said to possess 300 alternations per second. 

ALTERNATIONS, COMPLETE— A change in the direction 
of a current in a circuit from its former direction and 
back again to that direction. A complete to-and-fro 
change. 

Complete alternations are sometimes indicated by the 
symbol. 0^ 

ALTERNATOR — A name commonly given to an alternate 
current dynamo. 

AMALGAM — A combination or mixture of a metal with 
mercury. 

AMEER~A resinous substance, generally of a transparent, 
yellow color. 

AMMETER — A form of galvanometer in which the value of 
the current is measured directly in amperes. 

AMMETER, MAGNETIC- VANE— An ammeter in which the 
strength of a magnetic field produced by the current 
that is to be measured is determined by the repulsion 
exerted between a fixed and movable iron vane, placed 
:n said field and magnetized thereby. 

AMxMETER, PERMANENT-MAGNET— A form of ammeter 
in which a magnetic needle is moved against the field 
of a permanent magnet by the field of the current it ^ 
measuring. 

AMPERAGE — The number of amperes passing in a given 
circuit. 



307 ARC 

AMPERE — The practical unit of electric current. 

Such a current as would pass with an electromotive 
force of one volt through a circuit whose resistance is 
equal to one oinn. 

A current of such strength as would deposit .005084 
grain of copper per second. 

AMPERE-TURN— (See Turn, Ampere). 

ANION — The electro-negative radical of a molecule. 

An anion is that group of atoms of an electrically de- 
composed of electrolyzed molecule which appears at 

the anode. 

• 

ANNUNCIATOR, ELECTRO-MAGNETIC— An electric de- 
vit^e for automatically indicating the points or places 
at which one or more electric contacts have been closed. 

ANNUNCIATOR, HOTEL— An annunciator connected with 
the different rooms of a hotel. 

ANODE — The conductor or plate of a decomposition cell 
connected with the positive terminal of a batterj^ or 
other electric source. 

That terminal of an electric source out of which the 
current flows into the liquid of a decomposition cell. 

ARC— A voltaic arc. 

ARC — To form a voltaic arc. 

ARC, ALTERNATING—A voltaic arc formed by means of 
an alternating current. 

ARC, HISSING OF--A hissing sound attending the forma- 
tion of voltaic arcs when the carbons are too near to- 
gether. 



ARM 3U» 

AEC, VOLTAIC — The source of lig-ht of the electric arc 
lamp. 

ARM BRIDGE— One of the sections in a Wheatstone bridge 

for necessary resistance. 
ARM-CROSS— A transverse piece attached to a pole for the 

support of wires, 
ARM, ROCKER— An arm on v.'hich the bru-^hes of a dynamo 

or motor are mounted for the purpose of shifting thefr 

position on the commutator. 

ARMATURE— A mass of iron or other magnetizable mate- 
rial placed on or near1:he pole or poles of a magnet. 

ARMATURE, BI-POLAR — An armature of a dynamo-elec- 
tric machine the polarity of which is reversed twice in 
every revolution through the field of the machine. 

ARMATURE, DRUM — An armature of a dynamo-electric 
machine, in which the armature coils are ^\ound longi- 
tudinally over the surface of a cylinder or drum. 

AR:MATURE, DYXAMO-ELECTRIC machine— That part 
of a dynamo-electric machine in which the differences 
of potential which cause the useful currents are gen- 
erated. 

ARMATURE, POLARIZED— An armature which possesses 
a polarity independent of that imparted by the magnet 
pole near which it is placed. 

AR!N MATURE, RIXG — A dynamo-electric machine armature, 
the coils of which are wound on a ring-shaped core. 

ARMATURE, SPHERIC Ali— A dynamo-electric machine ar- 
mature, the coils of which are wound on a spherical 
Iron core. 



309 BAG 

ARRESTEE, LIGIITNTNG— A device by means of which 
the apparatus placed in any electric circuit is protected 
from the destructive effects of a flash or bolt of light- 
ninor. 

ASTATIC — Possessing no directive power. 

Usually applied to a magnetic or electro-magnetic 
device which is free from any tendency to take a defi- 
nite position on account of the earth's magnetism. 

ATMOSPHERE, AJN"— A unit of gas or fluid pressure equal 
to about 15 pounds to the square inch. 

ATTRACTION, MAGNETIC— The mutual attraction exert- 
ed between unlike magnet poles. 

AURORA BOREALIS— The Northern Light. Luminous 
sheets, columns, arches, or pillars of pale, flashing light, 
generally of a red color, seen in the northern heavens. 

AUTOMATIC CONTACT BREAKER— (See Contact Breaker, 
Automatic). 

AUTOMATIC CUT-OUT— (See Cut-Out, Automatic). 

B 

B — A contraction used in mathematical writings for the 
internal magnetization, or the magnetic induction, or 
the number off lines of force per squaire inch or per 
square centimetre in the magnetized material. 

B. A. OHM— (See Ohm, P. A.) 

B. W. G. — A. contraction for Birmingham wire gauge. 

BACK ELECTROMOTIVE FORCE— (See Force, Electromo- 
tive. Bacl<). 



BAT 310 

BALANCE, COULOMB'S TORSION— An apparatus to meas- 
ure the force of electric or magnetic repulsion between 
two similarly charged bodies, or between two similar 
magnet poles, by opposing to such force the torsion of 
a thin wire. 

The two forces balance each other; hence the origin 
of the name. 

B.^ LANCE, INDUCTION, HUGHES'— An apparatus for the 
detection of the presence of a metallic or conducting 
substance by the aid of induced electric currents. 

BALLS, PITH — Two balls of pith, suspended by conducting 
threads of cotton to insulated conductors, employed to 
show the electrification of the same by their mutual 
repulsion. 

BARS, BUS— Omnibus bars. (See Bars, Omnibus). 

BARS, OMNIBUS — Main conductors common to two or 
more dynamos in an electrical generating plant. 

The terms bus and omnibus bars refer to the fact 
that the entire or whole current is carried hy them. 

BATH, COPPER — An electrolytic bath containing a readily 
electrolyzable solution of a copper salt, and a copper 
plate acting as the anode, and placed in the liquid near 
the object to bo electro-plated, which forms the kath- 
ode. 

BATH, ELECTRO-PLATING -Tanks containing metallic 
solutions in which articles are placed so as to be elec- 
tro-plated. 

BATH, NICKEL — An electrolytic bath containing a readily 
electrolyzable salt of nickel, a plate of nickel acting as 
the anode of a battery and placed in the liquid near the 
object to be coated, which forms the kathode. 



311 BAT 

BATTEKY, CLOSED-CIRCUIT— A voltaic battery which 
may be kept constantly on closed-circuit without seri- 
ous polarization. 

BATTERY, ELECTRIC— A general term applied to the 
combination, as a single source, of a number of sepa- 
rate electric sources. 

BATTERY, GAS— A battery in which the voltaic elements 
are gases as distinguished from solids. 

BATTERY, LEYDEN JAR— The combination of a number 
of separate Leyden jars so ^ to act as one single jar. 

BATTERY, LOCAIi— A voltaic b^tttery used at a station on 
a telegraph line to operate the Morse sounder, or the 
registering or ^recording apparatus, at that point only. 

BATTERY, OPEN-CIRCUIT— A voltaic battery which is 
normally on open circuit, and which is used continu- 
ously only for comparatively small durations of time 
on closed-circuit. 

BATTERY, PLUNGE- A number of separate voltaic cells 
connected so as to form a single cell or electric source, 
the plates of which are so supported on a horizontal 
bar as to be capable of being simultaneously placed 
in, or removed from, the exciting liquid. 

BATTERY, PRI:MARY— The combination of a number of 
separate primary cells so as to form a single source. 

BATTERY, SECONDARY— The combination of a number 
of separate secondary or storage cells, so as to form a 
single electric source. 

BATTERY SOLUTION— (See Solution, Battery). 

BATTERY, STORAGE— A number of separate storage cells 
connected so as to form a single electric source. 

BATTERY, VOLTAIC— The pombination, as a single source, 
of a number of separate voltaic cells. 



BOM 312 

BELL MAGNETO ELECTRIC— A • bell rung by tlie move- 
menit of the arina.ture of an- electro magnet. 

BELL, TELEPHONE-CALT^A call bell used to call a cor- 
respondent to the telephone. 

BI-POLAK— Ha^-ing two poles. 

BLASTTXC, ELECTETC— The electric ignition of powder 
or other explosive material in a blast. 

BLOCK, BIaANCH — A device employed in electric wiring 
for taking off a branch from a main circuit. 

BLOCK, EUSE — A block containing a safety iuse or fuses 
for incandescent light circuits. 

BOAELj, HANGEE— a form of board provided for the ready 
placing or removal of an arc lamp from a circuit. 

BOAHD, ISrULTIPLE SWITCH— A board to which the nu- 
merous circuits employed in systems of telegraph}', 
telephony, annunciator or electric light and power cir- 
cuits are connected. 

20AED, SWITCH— A board pro\dded wdth a smtch or 
switches, by means of which electric circuits connected 
therewith may be opened, closed, or interchanged. 

BOBBIN. ELECTRIC— An insulated coil of wire for an 
electro-magnet. 

BODY, ELECTRIC RESISTANCE OF— The resistance of 
the humian body measured from hand to Jiand varies 
from 3,000 ohms to 15,000 ohms. 

BOLO^IETER — An apparatus devised by Langley for meas- 
uring small differences of temperature. 

BOMBARDMENT, MOLECULAR— The forcible rectilinear 
projection from the negative electrode, of the gaseous 
molecules cf the residual atmospheres of exhausted ves- 
sels on the passage of electric discharges. 



313 BRI 

BORE, ARMATURE — The space provided between the pole 
pieces of a dynamo or motor for the rotation of the 
armature. 

BOX, DISTRTCT-CALL— xV box by means of which an elec- 
tric signal is automatically sent over a telegraphic line 
and received by an electro-magnetic device at the other 
end of the line. 

BOX, FIRE-ALARM SIGNAL— A signal box provided for 
the purpose of automaticalh'' sending an alarm of fire. 

BOX, FUSE — The box in which the fuse-wire of a safety- 
fuse is placed. 

BOX, JUXCTIOX — A moisture-proof box provided in a sys- 
tem of underground conductors to leceive the termi- 
nals of the feeders, in which connection is made be- 
tween the feeders and the mains, and from which the 
* current is distributed to the individual consumer. 

BOX, RESISTANCE — A box containing a number of sepa- 
rate coils of known resistances employed for determin- 
ing the value of an unknovvn resistance, and for other 
purposes. 

BRAKE, ELECTRO-MAGNETIC— A brake for car wneels, 
the braking power for which is either derived entirely 
from electro-magnetism, or is thrown into action by 
electro-magnetic de\dces. 

BRAKE, PRONY — A mechanical device for measuring the 

power of a driving shaft. 
BRANCH-BLOCK— (See Block, Branch). 
BREAKER, CIRCUIT— Any device for breaking a circuit. 

BRIDGE-ARMS -(See Arms, Bridge or Balance). 

21 



BRU 314 

BEIDGE, ELECTEIC— A device for measurino- the value of 
electric resistances. 

The electric brirlge is also called the Electric 13alanc§: 

BEIDGE, MAGNETIC— An apparatus invented by Edison 
for measuring" magnetic resistance, similar in principle 
to Wheatstone's electric bridg-e. 

BRUSH, DISCHARGE— (See Discharge, Brush). 

BRUSH-HOLDERS EOR DYNAMO-ELECTRIC J\L\CIIINES 
— Devices for supporting the collecting JDrushes of dy- 
namo-electric machines. 

BRUSH ROCKER— (See Rocker, Brush). 

BRUSHES, ADJUSTMENT' OF DYNAMO-ELECTRI6 MA- 
CHINES — Shifting the brushes into the required posi- 
tion on the commutator cylinder, either non-automatic- 
ally by hand, or automatically by the current itself. 

BRUSHES, CARBON, FOR ELECTRIC MOTORS— Plates of 
carbon for leading current to electric motors. 
These are generally known simply as brushes. 

BRUSHES, LEAD OF— The angle through which the 
brushes of a dynamo-electric machine must be moved 
forward, or in the direction of rotation, in order to 
diminish sparking and to get the best output from the 
dynamo. 

BRUSHES OF DYNAMO-ELECTRIC MACHINE— Strips of 
metal, bundles of wire, slit plates of metal, or plates of 
carbon, that bear on the commutator cylinder of a 
dynamo-electric machine, and carry off the current 
generated. 



315 C. G. S. 

BUCKLING — Irreg-ularities in ^he shape of the surfaces of 
the plates of storage cells, following- a too rapid dis- 
charg*e. 

BUG — A term originally employed in quadruplex telegra- 
phy to designate any fault in the operation of the ap^ 
paratus. 

BUNSEN VOLTAIC CELL— (See Cell ,Voltaic, Bunsen's). 

BURGLAR ALARM ANNUNCIATOR— (See Annunciator^ 
Burglar Alarm). 

BURNER, AUTOMATIC-ELECTRIC— An electric device for 
both turning on the gas and lighting it, and turning it 
off, by alternately touching different buttons. 

BUS— A word generally used instead of omnibus. 

BUS-BARS— f See Bars, Bus). 

BUTTON, CARBON— A resistance of carbon in the form of 
a button. 

BUTTON, PUSH — A device for closing an electric circuit by 
the movement of a button. 

BUZZER, ELECTRIC— A call, not as loud as that of a bell,, 
produced by a rajjid automatic make-and-break. 



C — An abbreviation for centigrade. 

C — A contraction for current. 

C. C. — A contraction for cubic centimetre. 

C. G. S. UNITS — A contraction for centimetre-gramme-sec- 
ond units. 



CAL 316 

C. P. — A contraction for candle power. 

CABLE — To send a telegraphic dispatch, by means of a 

cable. 
CABLE, BUNCHED — A cable containing more than a single 

wire or conductor. 

CABLE, CAPACITY OF— The ability of a wire or cable to 
permit a certain quantity of electricity tc>be passed 
into it before acquiring a given dift'erence of potential. 

CABLE, ELECTKIC— The combination of an extended 
length of one or more separately insulated electric con- 
ductors, covered externally vnth a metallic sheathing 
or armor. 

CABLE, SUBMARINE— A cable designed for use under 

. water. 
CABLEGEAM — A message received by means of a subma- 
rine telegraphic cable. 

CALIBRATE — To determine the absolute or relative value 
of the scale divisions, or of the indications of any elec- 
trical instrument, such as a galvanometer, electrome- 
ter ,voltameter, wattmeter, etc. 

CALL-BEIX, MAGNETO-ELECTBIC— An electric call-bell 
operated by currents produced by the motion of a coil 
of wire before the poles of a permanent magnet. 

CALOEIE, GBEAT— The amount of heat required to raise 
the temperature of one kilogramme of water from 
degree C. to 1 degree C. 

CALOPJE, S:MALL- — The amount of heat required to raise 
tue tem.peratnre of one gramme of water from degree 
C, to 1 degTee C. 



317 . CAU 

CANDLE — The unit of photometric intensity. Such a light 
as would be produced by the coQsumx-»tion of two grains 
of a standard candle per minute. 

CAXDLE, JABLOCHKOFF— An electric arc light in which 
the two carbon electrodes are placed parallel lo each 
other and maintained a constant distance apart by 
means of a stieet of insulating material placed betv/een 
them. 

CANDLF-POWEK— (See Power, Candle). 

CAOUTCHOUC, OR IXIJIA-RUBBER— A resinous substance 
obtained from the milky juices of certain tropical trees. 

CAPACITY, ELECTROSTATIC— The quantity of electricity 
Avhich must be imparted to a given body or conductor 
as a charge, in order to raise its potential a certain 
amount. 

CAPACITY, ELECTROSTATIC, Ul>n:T OF— Such a capacity 
of a conductor or condenser that an electromotive force 
of one volt will charge it with a quantity of electricity 
equal to one coulomb. The farad. 

CAPACIl'Y, SPECIFIC INDUCTIVE— The ability ot a di- 
electric to permit induction to take place tnrough its 
mass, as compared with the ability possessed by a mass 
of air of the same dimensions and thickness, under pre- 
cisely similar conditions. 

CARBON — An elementary substance which occurs naturally 
in three distinct allotropic forms, viz: charcoal, graph- 
ite and the diamond. 

CARBON POINTS— (See Points, Carbon). 



CAU * 318 

CAEBOX TEA?s"SMlTTEE FOR TELEPHONES— (See 
Transmitter, Carbon, for Telephones). 

CARBONIXG LAVlPS— (See Lamps, Carboning). 

CARBOXJZE — To reduce a earbonizable material to carbon. 

CAPBOXS, AETIFICIAIi-— Carbons obtained by the carboni- 
zation of a mixture of pulverized carbon with diiferent 
carboniza}>]e liquids. 

CAPBOXS, COPEI)--A cylindrical carbon electrode for an 
arc lamp that is molded around a central core of char- 
coal, or other softer carbon. 

CAPBOXS, ELASIITXG PPOCESS FOP— A process for im- 
proving* the electrical uniformity of the carbon conduc- 
tors employed in incandescent lighting, by the deposi- 
tion of carbon in their pores, and over their surfaces at 
those places where the electric resistance is relatively 
great. 

CAPD, COMPASS — A card used in the mariner's compass, 
on which are marked the four cardinal points of the 
compass X, S, E and W, and these again divided into 
thirty-tw^o points called Rhumbs. 

CAPDEW YOLT^IETEP— (See Voltmeter, Cardew). 

CATAPHOPESIS — A term sometimes employed in place of 
electric osmose. (See Osmose, Electric). 

CATHOBE — A term sometimes used instead of Kathode. 

CAUTEPTZATIOX, l^LECTPTC— Subjecting to cauterization 
by means cf a wire electrically heated. 



319 OEL 

CAUTERY, ELECTRIC— An instrument used for electrio 
craiterization. "Jn electro-theraT)eutics, the application 
of vaiio'.isl}' shaped platinum wires heated to incan- 
descence by the electric current in place of a knife, for 
remo\ing" diseased growths, or for stopping- hemor- 
rhag-es. 

CELL, ELECTEOLYTIC— A cell or vessel containing- an 
electrolyte, in which electrolysis is carried on. 

CELI:, POROUS — A jar of ung-lazed earthenware, emj)loyed 
in double-fiuid voltaic cellSj to Iceep the two liquids sep- 
arated. 

CELL, SECONDARY — A term sometimes used instead of 
storage cell. 

CELL, SECONDARY OR STORAGI], CAPACITY OF— The 
product of the current m amperes, by the number of 
hours the battery is capable of furnishing said current, 
when fully charged, until exhausted. 

CELL, SELENTIL^L — A cell consisting of a mass of selenium 
fused in between two conducting wires or electrodes of 
platinized silver or other suitable metal. 

CELL, ST07LAGE— A single one of the cells required to 
form a secondary battery. 

CELL, VOLTAIC— The combination of two metals, or of a 
metal and a metalloid, which, when dipped into a liquid 
or liquids called electrolj^tes, and connected outside the 
liquid or liquids by a conductor, will produce a current 
of electricity. 

CELL, VOLT-A.IC, BICHROMATE— A zinc-carbon couple 
used with an electrolyte known as electropoion, a solu- 
tion of bichromate of potash and sulphuric acid in 
water. 



CEL 320 

CELL, VOLTAIC, BUNSEN'S— A zinc-carbon couple, the 
elements of which are immersed respectively in electro- 
lytes of dilute sulphuric and strong- nitric acids. 

CELL, VOLTAIC, CLOSED-CIRCUIT— A voltaic cell that 
can be left for a considerable time on a closed circuit of 
comparatively small resistance without serious polari' 
zation. 

CELL, VOLTAIC, CONTACT THEOEY OF— A theory which 
accounts for the production of difference of potential 
or electromotive force in the voltaic cell by the contact 
of the elements of the voltaic couple with one another 
by means of the electrolyte. 

CELL, VOLTAIC, DANIELL'S— A zinc-copper couple, the 
elements of which are immersed respectively in electro- 
lytes of dilute sulphuric acid, and a saturated solution 
of copper sulphate. 

CELL, VOLTAIC, DOUBLE-FLUID— A voltaic cell in which 
two separate liuids or electrolytes are employed. 

CELL, VOLTAIC, DEY— A voltaic cell in which a moist ma- 
terial is used in place of the ordinary fluid electrolyte. 

CELI<, VOLTAIC, FULLEK'S :MERCUEY BICHROMATE— 
A zinc-carbon couple imn-ersed in an electrolyte of elec- 
tropoion liquid. In w^hioh ithe zinc is in contact with 
liquid mercury. 

CELL, VOLTAIC, GRAVITY— A zinc-copper couple, the ele- 
ments of which are employed with electrolytes of dilute 
sulphuric acid or dilute zinc sulphate, and a concentra- 
ted solution i>»f copper sidphate respectively. 



321 CHA 

CELL, VOLTAIC, GKOVE— A zinc-platinum couple, the ele- 
ments of which are used with electrolytes of sulphuric 
and nitric acids respectivel5\ 

CELL, VOLTAIC, LECLAXCHE— A zinc-carbon couple, the 
elements of which are used in a solution of sal-ammo- 
r.iac and a finely divided \ayec of black oxide of man- 
ganese respectively. 

CELL, VOLTAIC, OPEX-CIKCUIT— A voltaic cell that can 
7iot be kept on closed circuit, with a comparatively 
small resistance, for any considerable time without 
serious polarization. 

CELL, VOLTAIC, POLAEIZATIOX OF— The collection of a 
g-as, generally hydrogen, on the surface of the negative 
element of a voltaic cell. 

CELL. VOLTAIC, SILVEE CHLOEIDE— A zinc and silver 
couple immersed in electrolytes of sal-ammoniac or 
common salt, in which chloride of silver is used as the 
depolarizer. 

CELL, VOLTAIC, SMEE— A zinc-silver couple used with an 
electrolyte of dilute sulphuric acid. 

CELL, VOLTAIC, STANDARD, CLARK'S— The form of 
standard cell designed by Latimer Clark, having an 
E. M. F. of 1.438 volts at 57 degrees F. 

CHARACTERISTIC CURVE— (See Curve, Characteristic). 

CHARGE, DISSIPATION OF— The gradual but final loss of 
any charge by leakage, which occurs even in a well in- 
sulated conductor. 



CIR 322 

CIIAPtGE, DISTEIBUTIOX OF— The variations that exist 
In the density of an electrical charge at different por- 
tions of the surface of all insulated conductors except 
spheres. » 

CHAEGE, ELECTETC— The quantity of electricity that ex- 
ists on the surface of an insulated electrified conductor, 

CHAEGE, EESIDUAT. — The charge possessed by a charged 
Leyden jar for a few moments after it has been disrapt- 
zTelj discharged by the connection of its opposite coat- 
ings. 

CHAEGE, EETUEX — A charge induced in neighboring con- 
ductors by a discharge of lightning. 

CHAEGIXG ACCOIULATOES— Sending an electric current 
into a storage battery for the purpose of rendering it 
an electric source. 

CHOKIXG COTL— (See Coil, Choking). 

CIECUIT, CLOSED — A circuit is closed, completed, or made 
when its conducting continuity is such that the current 
can pass. 

CIECUIT, CLOSED-MAGNETIC— A magnetic circuit whic& 
lies wholly in iron or other substance of high magnetic 
permeability. 

CIECUIT, CONSTANT-CUEEENT— A circuit in which the 
current or number of amperes is maintained constant 
notwithstanding changes occurring in its resistance. 

CIECUIT, CONSTANT POTENTIAL— A circuit, the poten- 
tial or number of volts o? which is maintained approxi- 
mately constant. 



323 CIR 

CIECUIT, EARTH— A circuit in which the ground or earth 
forms part of the conducting* Dath. 

CIRCUIT, ELECTliTC— The path in which electricity circu- 
lates or posses from a given point, a>r?und or through a 
conducting path, back again to its starting point. 

CIRCUIT, EXTERNAL— That part of a circuit which is ex- 
ternal to, or outside the electric source. 

CIRCUIT, GROUND— A circuit in which the ground forms 
part of the path through which the current passes. 

CIRCUIT, INDUCTIVE— Any circuit in which induction 
takes place. 

CIRCUIT, INTERNAL— That part of a circuit which is in- 
cluded within the electric source. 

CIRCUIT, LOCAL-BATTERY— The circuit, in a telegraphic 
system, in which is placed a local battery as distin- 
guished from a main battery. 

CIRCUIT, AIAGNETIC— The path through which the lines 
of magnetic force pass. 

CIRCUIT, METALLIC— A circuit in which the ground is not 
employed af, any part of the path of the current, metal- 
lic conductors being employed throughout the entire 
circuit. 

CIRCUIT, MULTIPLE— A compound circuit, in which a 
number of separate sources or separate electro-receptive 
devices, or both, have all their positive poles connected 
to a single positive lead or conductor, and all their neg- 
ative poles to a single negative lead or conductor. 



CIR 324 

CIECUIT, MULTlPLE-SEPtlES— A compound circuit in 
which a number of separate sources, or separate elec- 
tro-receptive devices, or both, are connected in a num- 
ber of separate groups in series, and these separate 
groups subsequently connected in multiple. 

CIECUIT, OPEN— A broken circuit. A circuit, the con- 
ducting* continuity of which is broken. 

CIKCUIT, KETUBN— That part of a circuit by which the 
electric current returns to the source. 

CIRCUIT, SERIES—A compound circuit in which the sep- 
arate sources, or the separate electro-receptive devices, 
or both, are so placed that the current produced in 
each, or passed throusfh each, passes successively 
through the entire circuit from the first to the last. 

CIRCUIT, SERIES-MULTIPLE— x\ compound circuit, in 
which a number of separate sources, or separate elec- 
tro-receptive devices, or both, are connected in a num- 
ber of separate groups in multiple-arc, and these sepa- 
rate groups subsequently connected in series. 

CIRCUIT, SHORT— A shunt, or by-path, of comparatively 
small resistance, around the poles of an electric source, 
or around any portion of a circuit, by which so much 
of the current passes through the new path, as virtualh^ 
to cut out the part of the circuit around which it is 
placed, and so prevent it from receiving an appreciable 
current. 

CIRCUIT, SHUNT— A branch or additional circuit provided 
at any part of a circuit, through which the current 
branches or divides, part flowing through the original 
circuit, and part through the new branch. 



325 COI 

CLARK'S STANDARD VOLTAIC CELL— (See Cell. Voltaic, 
Standard, Clark's). 

CL;e:aRAXCE-SPACE— (See Space, Clearance). 

CL]i?ATS, ELECTRIC— Suitably shaped pieces of wood, 
porcelain, hard rublDcr or other non-conducting material 
used for fastening- and supporting electric conductors 
to ceilings, walls, etc. 

CLOCK, ELECTRIC— A clock, the works of which are mov- 
ed, controlled, regulated or wound, either entirely or 
partially, by the electric current. 

CLUTCH, CARBON, OF ARC LAMP- A clutch or clamp at- 
tached to the rod or other support of the carbon of an 
arc lamp, provided for gripping or holding the carbon. 

CODE,. CIPHER — A code in which a number of words or 
phrases are represented by single words, or by arbitrary 
words or syllables. 

COIL, CHOKING — A coil of wire so wound on a core of iron 
as to possess high self-induction. 

COIL, IMPEDANCE— A term sometimes applied to a chok- 
ing-coil. 

COIL, INDUCTION — An apparatus consisting of two paral- 
lel coils of insulated wire employed for the production 
of currents by mutual induction. 

COIL, INDUCTION, MICROPHONE— An induction coil, in 
which the variations in the circuit of the primary are 
obtained by means of microphone contacts. (See Mi- 
crophone). 

colli, KICKING — A term sometimes applied to a Choking- 
Coil. 



COM 326 

UOJL, MAGNET — A coil of insulated wire surrounding the 
core of an electro-magnet, and through which the mag- 
netizing current is passed. 

COIL, PKIMATiY — That coil or conductor of an induction 
coil or transformer, through which the rapidl^^ inter* 
rupted or alternate inducing currents are sent. 

COTL, EESTSTAXCE— A coil of wire of known electrical 
resistance employed for measuring resistance. 

COIL, RESISTANCE, STANDARD— A coil the resistance of 
which is that of the standard ohm or some multiple or 
sub-multiple thereof: 

COTL, RUIIMKORFF — A term sometimes applied to any in- 
duction coil, the secondary of which gives currents ot 
higher electromotive force than the primary. 

COIL, SECONDARY— That coil or conductor of an induc- 
tion coil or transformer, in which alternating currents 
are induced by the rapidly interrupted or alternating 
currents in the x^^'iniary coil. 

COTL, SHUNT — A coil placed in a derived or shunt circuit. 

DOIL, SPARK — A coil of insulated wire connected with the 
main circuit in a system, of electric gas-lighting, the 
extra spark produced on breaking the t^ircuit of which 
is employed for electrically igniting gas jets. 

COILS, ARMATURE, OF DYNAMO-ELECTRIC MACHINE 

— The 'vioils, strips or bars that are wound or placed on 
the armature core. 
COMMERCIAL EFFICIENCY— (See Efficiency, Commercial). 

COMMERCIAL EFFICIENCY OF DYNAMO— (See Efficien- 
cy, Commercial, of Dynamo). 



327 COM 

COAOrUTATlOX, DIAMETER OF— In a dynamo-electric 
machine a diameter on the commutator cylinder on one 
side of which the difOerences of potential, produced by 
the movement of the coils through the magnetic field, 
tend to produce a current in a direction opposite fo 
those on the other side, 

COMMUTATOE — In general, a device for changing the di- 
rection of an electric current. 

COMMUTATOPi, DYNAMO-ELECTRIC MACHINE— That 
part of a dynamo- electric machine which is designed to 
cause the alternating currents produced in the arma- 
ture to flow in one and the same direction in the ex- 
ternal circuit. 

COMPASS, AZIMUTH— A compass used by mariners for 
measuring the horizontal distance of the sun or stars 
from the magnetic meridian. A mariner's Compass. 

COMPASS, INCLINATION"- A magnetic needle moving 
freely in a single vertical plane, and emploj^ed for deter- 
mining the angle of dip at any place. 

CO:NrPONENT, HORIZONTAL, OF EARTH'S jSEAGNETISM 
— That portion of the earth's directive force which acts 
in a horizontal direction. That portion of the earth's 
magnetic force which acts to produce motion in a com* 
pass needle free to move in a horizontal plane only. 

COMPOUND-WINDING OF DYNAMO-ELECTRIC MA- 
CHINES— (Sec \Alnding, Compound, of Dynamo-Elec- 
tric Machines). 

COMPOUxN"D-WOrND DYNAMO-ELECTRIC MACHINE— 
(See Machine. Dynamo-Electric, Compound-Wound). 



C0:>'' 328 

COMPOUND- WOUND :M0T0E— (See Motor, Compound- 
Wound). 

CONDFXSEK \ device for increasing the capacity ot an 
insulated conductor by bringing- it near another insu- 
lated 'earth-ccnnected conductor, but separated there- 
from by any medium that will readily permit induction 
to take place through its mass. 

COXDENSEK, CAPACITY OF— The quantity of electricity 
in coulombs a condenser is capable of holding before its 
potential in volts is raised a given amotmt. 

CONDUCT — To i)ass electricity through conducting sub- 
stances. 

CONDUCTANCE — A word sometimes used in place of con- 
ducting power. Conductivity. 

CONDUCTING POWEE— (See Power, Conducting). 

CONDUCTION, ELECTEOLYTIC— A term sometimes em- 
ployed to indicate the passage of 'electricity through 
an electrolyte. 

CONDUCTmTY, ELECTEIC— The reciprocal of electric 
resistance. 

CONDUCTOE— A substance which will permit the so-called 
passage of an electric current. A substance which pos- 
sesses the ability of determining the direction in whicB 
electricity shall pass through the ether or other dielec- 
tric surrounding it. 

CONDUCTOE, LIGIITNING — A term sometimes used for a 
lighlning rod. 



i529 CON 

CONDUCTORS, SERVICE—Conductors employed in sys- 
tems of incandescent lig-hting- connected to the street 
mains and to the electric apparatus placed in the sepa- 
rate building's or areas to be lig-hted. 

CONDUIT, TJNDEEGEOTJND ELECTRIC— An underground 
passageway or space for the reception of electric wires 
or cables. 

CONNECT — To place or bring- into electric contact. 

CONNECTOR — A. device for readily connecting or joining" 
the ends of two or more wires. 

CONSEQUENT POLES— (See Poles, Consequent). 

CONSERVATION OF ENERGY— (See Energy, Conservation 
of). 

CONSTANT-CURRENT— (See Current, Constant). 

CONSTANT-CURRENT CIRCUIT— (See Circuit, Constant 
Current). 

CONSTANT POTENTIAL— (See Potential, Constant). 

CONSTANT-POTENTIAL CIRCUIT— (See Circuit, Con- 
stant-Potential) . 

CONTACT-BREAKER, AUTOMATIC— A device for causing- 
an electric current to rapidly make and break its own 
circuit. , 

CONTACT, METALLIC— A contact of a metallic conductor 

produced by its coming* into firm connection with an* 

other metallic conductor. 
22 



COK 330 

CONTACT, SLIDING— A contact connected with one part 
of a circnit that closes or completes an electric circuit 
by being- slid over a conductor connected with another 
part of the circuit. 

CONTROLLER— A mag-net, in the Thomson-Houston sys- 
tem of automatic regulation, whose coils are traversed 
by the main current, and by means of which tlie regu- 
lator magnet is automatically thrown into or out of 
the main circuit on changes in the strength of the cur- 
rent passing. 

CONVECTION, ELECTROLYTIC— A term proposed bv 
Helmholtz to explain the apparent conduction of elec- 
tricity by an electrolj'te, without /consequent decom- 
position. 

CONVERTER— The inverted induction coil employed in 
systems of distribution by means of alternating- cur- 
rents. A term sometimes used instead of transformer. 

CONVERTER, EFFICIENCY OF— The efficiency of a trans- 
former. 

CONVERTER, PTEDGEHOG— A form of transformer. (See 
Transformer, Hedgehog). 

COPPER, STRAP — Copper conductors in the form of straps 
or flat bars. 

CORD, ELECTRIC— A flexible, insulated electric conductor, 
g-enerally containing at least two parallel wires. 

CORE ,AR:NLATUKE, H— An armature core the shape of tiie 
letter H, generally known as the shuttle armature, and 
sometimes as the g-irder armature. 



331 COU 

COEE, ARMATUKE, LAMINATION OF— The subdivision of 
the core of the armature of a dynamo-electrie machine 

\ into separate insulated plates or strips for the purpose 
of avoiding eddy or Foucault currents. 

COEE. ARMATURE, OF DYNAMO-ELECTRIC MACHINE— 
The iron core, on, or around, which the armature poils 
of a dynamo-electric machine are wound or placed. 

CORE, ARMATURE, VENTILATION OF— Means for pass- 
ing* air through the armature cores of dynamo-electric 
machines in order to prevent undue accumulation of 
heat. 

CORE, LAMINATED— A core of iron which has been divid- 
ed or laminated, in order to avoid the injurious produc- 
tion of Foucalt or eddy currents. 

CORE, STRANDED, OF CABLE— The conducting \%dre or 
core of a cable formed of a number of separate conduc- 
tors or wires instead of a single conductor of the same 
weight per foot as the combined conductors. 

CORED CARRONS— (See Carbons, Cored). 

COULO^IB — Such a quantity of electricity as would pass in 
one second in a circuit whose resistance is one ohm, 
under an electromotive force of one volt. 

COUNTER- ELECTROMOTIVE FORCE- (See Force, Elec- 
tromotive, Counter). 

COUPLE, ASTATIC— Two magnets of exactly equal 
strength so placed one over the other in the same ver- 
tical plane as to completely neutralize each other. 



CUR 332 

COUPLE, MAGNETIC— The couple which tends to turn a 
magnetic needle, placed in the earth's field, into the 
plane of the magnetic meridian. 

COUPLE, THERMO-ELECTRIC— Two dissimilar metals 
which, when connected at their ends only, so as 
to form a completed electric circuit, will produce a 
difference of potential, and hence an electric current, 
when one of the ends is heated more than the other. 

COUPLE, VOLTAIC— Two materials, usually two dissimilar 
metals, capable of acting- as an electric source when 
dipped in an electrolyte, or capable of producing* a dif- 
ference of electric potential by mere contact. 

CROSS ARM— (See Arm, Cross). 

CROSS, ELECTRIC— A connection, generally metallic, acci- 
dentally established between two conducting lines. 

CRUCIBLE, ELECTRIC— A crucible in which the heat of 
the voltaic arc, or of electric incandescence, is employed 
either to perform difScult fusions, or for the purpose of 
effecting the reduction of metals from their ores or the 
formation of alloys. 

CUP, POROI'S— A porous cell. 

CURRENT, ALTERNATING— A current which flows alter- 
nately in opposite directions. A current whose direc- 
tion is rapidly reversed. 

CURRENT, CONSTANT— A current that continues to flow 
for some time without varjdng in strength. 

CURRENT, CONTINUOUS— An electric current which flows 
in '>F)e and the same direction. 



333 CUR 

CURRENT DENSITY— The current of electricity which 
passes in any part of a circuit as compared with the 
area of cross-section of that part of the circuit. 

CURRENT, DIRECT— A current constant in direction, as 
distingniished from an alternating current. 

CURRENT, DIRECTION OF— The direction an electric cur- 
rent is assumed to take out from one pole of any source 
through the circuit and its translating* devices back to 
the source through its other pole. 

CUBRENT, ELECTRIC- The quantity of electricity which 
passes per second through any conductor or circuit. 
The rate at which a definite quantity of electricity 
passes or fiows through a conductor or circuit. 

CURRENT, GENERATION OF, BY DYNAMO-ELECTRIC 
MACITINP" — The difference of potential developed in 
the armature coils by the cutting of the lines of n\ag- 
netlc force of the field by the coils, during the rotation 
of the armature. 

CURRENT, INDUCED— The current produced in a conduc- 
tor by cutting lines of force. 

CURRENT, PULSATORl'— A current, the strength of which 
changes suddenly. 

CURRENT, ROTATING— A term applied to the current 
which results by combining a niimber of alternating 
currents, whose phases are displaced with respect to 
one another. 

CURRENT STRENGTH— The product obtained by dividing 
the electromotive force by the resistance. 

The current strength for a constant current accord- 
ing to Ohm's law is — E 
C equals — 
R 



CCJl 334 

CUREEXT, TO TEAXSFORM A— To change the electromo- 
tive force of a current by its passage through a convert- 
er or transformer. To convert a current. 

CUEEEXT, UXIT STEEXGTH OF— Such a strength of cur- 
rent that when passed through a circuit one centimetre 
in length, arranged in an arc one centimetre in radius, 
will exert a force of one dyne on a unit magnet pole 
placed at the center. This absolute unit is equal to ten 
amperes or practical units of current. 

CUEEEXTS, CO XM^ETED— Electric currents changed 
either in their electromotive force or in their strength, 
by passage through a converter or transformer. 

CUEElvN"TS, EDDY — Useless currents ]>roduced in the pole 
pieces, armatures, field-magnet cores of dynamo-electric 
machines or motors, or other metallic masses, either by 
their niotion througli magnetic fields, or by variations 
in tftie strength of electric currents flowing near them, 

CUEEEXTS, EXTEA— Currents produced in a circuit by 
the induction of the current on itself on the opening 
or closing of the circuit. 

CUEEEXTS, FOUCAULT— A name sometimes applied to 
eddy currents, especially in armature cores. 

CUEEEXTS, HEATIXG EFFECTS OF— The heat produced 
by the passage of an electric current through any cir- 
cuit. 

CUEEEXTS, SFNIPLE PEETODIC— Currents, the flow o9 
which is variable, both in strength and duration, and irt 
which the flow of electricity;, passing any section of the 
conductor, may be represented by a simple periodic 
curve. 



335 CUT 

CURVE, CnAEACTEETSTIC— A diagTam in which a curve 

is employed to represent the ratio oi: volts and am- 
pheres' in a dynamo or motor. 

CUEVE, CHARACTErJSTIC, OF PARALLEL TRANSFOR* 
MER — A curve so drawn that its ordinate and abscissa 
at any point represent the secondary electromotive 
force and the secondary current of a multiple connected 
trnnsformer, when the resistance of the secondary eir« 
cuit has a certain definite value. 

CURVE. PERMEABILITY— xA. curve representing- the mag- 
netic permeability of a magnetic substance. 

CURVE, SIMPLE-HARMONIC— The curve which results 
when a simple-harmonic motion in one line is com- 
pounded with a uniform motion in a straight line, at 
right ang-les thereto. 

A harmonic curve is sometimes called a curve of sines 
because the abscissas of the curve are proportional to 
the times, while the ordinates are proportional to the 
sines of the angles, which 5re themselves proportional 
to the times. 

CUT-OUT, A — A device by means of whi<6h an electro-re- 
ceptive device or loop may be thrown out of the circuit 
of an electric source. 

CUT-OUT, AUTOMATIC, FOR MULTIPLE-CONNECTEI> 
ELECTRO-RECEPTICE DEVICES— A device for auto- 
matically cutting an electro-receptive device, such as a 
lamp, out of the circuit of the leads. 

Automatic cut-outs for incandescent lamps, when 
connected to the leads in multiple-arc, consist of strips 
of readily melted metal called safety-fuses, which on 
the passage of an excessive current fuse, and thus auto- 
matically break the circuit in that particular branch. 



DEC 336 

CUTTING LmES OF FORCE— (See Force, Lines of Cutting) 

CYCLE — A period of time within which a certain series of 
phenomena regularly recur, in the same order. 

CYCLE, MACrNETIC— A single round of magnetic changes 
to which a magnetizable substance, such as a piece of 
iron, is subjected when it is magnetized from zero to a 
certain maximum magnetization, then decreased to 
zero, reversed and carried to a negative maximum, and 
then decreased again to zero. 



DAIMPEE — A metallic cylinder provided in an induction 
coil so as to partially or completely surround the iron 
core, for the purpose of varying the intensity of the 
currents induced in the secondary. 

DAMPING — The act of stopping vibratory motion such as 
bringing a swinging magnetic needle quickly to rest, 
so as to determine the amount of its deflection, without 
waiting until it comes to rest after repeated swingings 
to and fro. 

DEAD-BEAT — Such a motion of a galvanometer needle in 
which the needle moves shary^ly over the scale from 
point to point and comes quickly to rest. 

DECLTXATION — The variation of a magnetic needle from 
the true geographical north. 

DECLINATION, ANGLE OF— The angle which measures 
the deviation of the magnetic needle to the east or west 
of the true geographical norfh. 



337 BIE 

DECOMPOSITION, ELFXTEIC— Chemical decoinposition by 
means of an electric discharge or current. 

DEMAGNETIZATION — A process, g-enerally directly oppo- 
site to that for producing- a magnet, by means of which 
the magnet may be deprived of its magnetism. 

DENSITY, MAGNETIC— The strength of magnetism as 
measured by the number of lines of magnetic force 
that pass through a unit area of cross-section of the 
magnet, i. e., a section taken at right angles to the 
lines of force. 

DEPOSIT. ELECTPO-METALLURGICAL— The deposit of 
metal obtained by an^' electro-metallurgical process. 

DETECTOE, GEOUND— In a system of incandescent lamp 
distribution, a device placed in the central station, for 
shovs^ing by the candle-power of a lamp the approxi- 
mate location of a ground on the s^^stem. 

DEVICE, ELECTEO-EECEPTIYE— Various devices placed 
in an electric circuit, and energized by the passage 
through them of the electric current, 

DEVICE, TRANSLATING— A term embracing electro-re^- 
ceptive and magnefo-receptive devices. (See Device, 
Electro-Eeceptive) . 

DIAMAGNETIC — The property possessed by substances 
like bismuth, phosphorus, antimony, zinc and numerous 
others, of being apparently repelled when placed be- 
tween the poles of powerful magnets. 

DIELECTEIC — A substance which permits induction to 
tak^ place through its mass. 



DIS 338 

BTELECTETC, POLAPJZATTOX OF— A molecular strain 
produced in the dielectric of a Leyden jar or other con- 
denser> by the attraction of the electric charges on its 
opposite faces, or by the electrostatic stress. 

DI^niEH — A choking coil or resistance employed for regu- 
lating* the potential of the feeders, which usually carry 
incandescent lamps. 

DIP, MAGXETIC— The deviation of a magnetic needle from 
a true horizontal position. The inclination of the mag- 
netic needle towards the earth. 

DIEECT CUREEXT— (See Current, Direct). 

DIEECT-CUEEEXT ELECTEIC MOTOE— (See Motor. Elec- 
tric, Direct-Current). 

DIEECTIOX OF LIXES OF FOECE— (See Force, Lines of, 
Direction of). 

DISC, AEAGO'S — A disc of copper or other non-magnetic 
metallic substance, which, when rapidly rotated under 
a magnetic needle, supported independently of the disc, 
causes the needle to be deflected in the direction of 
rotation, and, when the velocity of the disc is sufficient- 
ly great, to rotate with it. 

DISC, FAEADAY'S — A metallic disc movable in a magnetic 
field on an axis parallel to the direction of the field. 

DISCHAEGF>— The equalization of the difference of poten- 
tial between the terminals of a condenser or source, on 
their connection by a conductor. 

DISCHAEGE, BEUSH— A faintly luminous discharge that 
occurs from a pointed positive conductor. 



339 BIS 

DISCTTARGE, DISEUPTIVE— A sudden, and more or less 
complete, discharge that takes place across an inter- 
vening* non-conductor or dielectric. 

DISCHARGE, LUMINOUS EFFECTS OF— The luminous 
phenomena attending- and produced by an electric dis- 
charg-e. 

DISCHARGE, OSCILLATING— A njiimber of successive dis- 
charges and recharg-es w^hich occur on the disruptive 
discharge of a Lej^den jar, or condenser. 

DISCHARGE, VELOCITY. OF— The time required for the 
passage of a discharge through a given length of con- 
ductor. 

DISCHARGER, UNIVERSAL— An apparatus for sending 
the discharge of a powerful Leyden battery or condens- 
er in any desired direction. 

DISCONNECT— To break or open an electric circuit. 

DISTANCE, SPARKING— The distance at which electrical 
sparks will pass through an intervening air space. 

DISTILLATION, ELECTRIC— The distillation of a liquid in 
which the effects of heat are aided b}^ an electrification 
of the liquid. 

DISTRIBUTION, CENTER OF— In a system of multiple- 
distribution, any place where branch cut-outs and 
switches are located in order to control communication 
therewith. The electrical center of a system of distxi- 
liution as regards the conducting network. 

DISTRIBUTION OF ELECTRICITY— (See Electrcity, Dis- 
tribution of). 



DYN 340 

DISTRIBUTION OF ELECTRICITY BY CONSTANT PO- 
TENTIAL CIlCCITri'— (See Electricity, Multiple Distri- 
bution of, by Constant Potential Circuit). 

DOUBLE-CARBON ARC LAMP— (See Lamp, Electric Arc, 
Double-Carbon ) . 

DOUBLE-EIUID VOLTAIC CELL— (See Cell, Voltaic, Dou- 
ble-Fluid). 

DOUBLE-TOUCH, MAGNETIZATION BY— A method for 
producing magnetization by the simultaneous touch of 
two magnet poles. 

DROP, ANNUNCIATOR— A movable signal operated by an 
electro-magnet, and placed on an annunciator, the drop- 
ping of which indicates the closing or opening of the 
circuit with which the electro-magnet is connected. 

DROP, AUTOMATIC— A device for aiitomaticallv closino- 
the circuit of a bell and holding it closed until stopped 
bj^ resetting a drop. ' 

DRUM ARMATURE— (See Armature, Drum). 

DRY VOLTAIC CELL- (See Cell, Voltaic, Dry). 

DUPLEX TELEGRAPHY— (See Telegfaphy, Duplex). 

DYEING, ELECTRIC— The application of. electricity eithef 
to the reduction or the oxidation of the salts used in 
dyeing. 

DYNAMICS, ELECTRO— That branch of electric science 
which treats of the action of electric currents on one 
another and on themselves or on magnets. 

DYNAMO — The name frequently applied to a dynamo-elec- 
tric machine used as a generator. 



341 DYN 

DTN-AMO, COMPOSITE FIELD— A dynamo whose field 
coils are series and separately excited. 

DYXAMO, COMPOUND-WOUND— A compound-wound dy- 
nam^o-electric machine. (See Machine, Dynamo-Elec- 
tric, Compound- Wound). 

DYN AMO-ELECTKTC MACHINE, BI-POLAE~(See Ma- 
chine, Dynamo-Electric, Bi-Polar). 

DYNAMO-ELECTEIC MACHINE, MULTIPOLAR— (See Ma- 
chine, Dynamo-Electric, Multipolar). 

DYNAMO, INDUCTOPt— A dynamo-electric machine for al- 
ternating* currents in which the diiferences of potential 
causing the currents are obtained by magnetic changes 
in the cores of the armature and field coils by the move- 
ment past them of laminated masses of iron inductors. 

DYNAMO, MULTIPHASE— A polyphase dynamo. (See Dy- 
namo, Poh'phase. Dynamo, Rotating Current). 

DYNAMO, POTiYPHASE— A dynamo producing two or 
more currents differing in phase. A name sometimes 
applied to a rotating current dynamo, (See Dynamo, 
Rotating Current). 

DYNAMO, PYBOMAGNETIC— A name sometimes applied 
to a pyromagnetic generator. 

DYNAMO. SEPARATELY EXCITED— A separately-excited 
dynamo-electric machine. 

DTr^AMO, SERIES — A series-wound dynamo-electric ma- 
chine. 

DYNAMO. SHUNT — A shunt-wound dynamo-electric ma- 
chine. 



EFF 342 

DY1S^4M0jV[ETFK, electro— a form of galvanometer for 
the measurement of electric currents. 

DYNE — The unit of force. The force which in one second 
can impart a Telocity of one centimetre per second to 
a mass of one gramme. 



E. — A contraction sometimes used for earth. A contraction 

sometimes used for electromotive force, or E. M. F., as 

in the well-known formula for Ohm's law, 

E 

C equals — 

R 

E. M. r. — A contraction generally used for electromotive 
force. 

p]ARTH-7A fault in a telegraphic or other line, caused by 
accidental contact of the line with the ground or earth, 
or with some conductor connected with the latter. 

EBONITE — A tough, hard, black substance, composed of 
india rubber and sulphur, which possesses high powers 
of insulation and of specific inductive capacity. 

EDDY CURRENTS— (See Currents, Eddy). 

EEL, ELECTRIC — An eel possessing the power of giving 
powerful electric shocks. The gyinnotus electricus. 

EFFECT, EDISON--An electric discharge which occurs be- 
tween one of the terminals of the incandescent, filament 
of an electric lamp, and a metallic plate placed near 
the filament but disconnected therefrom, as soon as a 
certain difierence of potential is reached between the 
lamp terminals. 






343 -EiFW 

EFFECT. FEEHANTI— An increase in the electromotive 
force, or difference of potential, of mains or conductors 
towards the end of the same farthest from the termi- 
nals that are connected with a source of constant pc5* 
tential. 

EFFECT, HALL — A transverse electromotive force, pro- 
duced by a magnetic field in substances undergoing' 
electric displacement. 

EFFECT, JOULE— The heating eifect produced by the pass- 
age of an electric current through a conductor, arising" 
merely from the resistance of the conductor. 

EFFECT, PELTIER— The heating effect produced by the 
passage of an electric current across a thermo-electric 
■junction or surface of contact .between two different 
metals. 

EFFECT, THEFtMO-ELECTETC— The production of an elec- 
tromotive force at a thermo-electric junction by a dif- 
ference of temperature between that junction and the 
other junction of the thermo-electric couple. 

EFFECT, THOMSON— The production of an electromotive 
force in unequally heated homogeneous conducting sub- 
stances. A. term also applied to the increase or decrease 
in the differences of temperature in an unequally heat- 
ed conductor, produced by the passage of an electrical 
current through the conductor. 

EFFECT, VOLTAIC— A difference of potential observed at 
the point of contact of two dissimilar metals. 



EFF 344 

EFFICIENCY, COMMERCIAL— The useful or available en- 
ergy produced divided by the total energy absorbed by 
any machine or apparatus. 
The Commercial Efficiency equals 

W W 

— equals 



M W+w+m, 

when W equals the useful or available energy; M equals 
the total energy; w, the energy absorbed by the ma- 
chine, and m, the stray power, or power lost in friction 
of bearings, etc., air friction, eddy currents, etc. 

I:FFICIENCY, COMMEECIAL, of dynamo— The useful 
or available electrical energy in the external circuit, 
divided by the total mechanical energy required to drive 
the dynamo that produced it. 

EFFICIENCY, ELECTRIC— The useful or available electric- 
al energy of anj^ source, divided by the total electrical 
energy. 

W 

The electric efficiency equals , where W, equals 

W-fw 

the useful or available electrical energy, and w, 
the electrical energy absorbed by the. machine. 

EFFICIENCY OF CONVERSION— The ratio between the 
energy present in any result and the energy expended 
in producing that result. 

EFFICIENCY, QUANTITY, OF STORAGE BATTERY— The 
ratio of the number of ampere-hours, taken out oi a 
storage or secondary battery, to the number of ampere- 
hours put in the battery in charging it, 



345 ELE 

EFFICIENCY, KEAL, OF STORAGE BATTERY— The ratio 
of the number of watt-honrs taken out of a storage 
battery, to the number of watt-hours put into the bat- 
tery in charging it. 

ELECTRIC— Pertaining to electricity. 
ELECTRIC ARC— (See Arc, Electric). 
ELECTRIC BATTERY— (See Battery, Electric). 
ELECTRIC BOBBIN— (See Bobbin, Electric). 
ELECTRIC BUZZER— (See Buzzer, Electric). 
ELECTRIC CANDLE— (Se^ Candle, Electric). 
ELECTRIC CHARGE— (See Charge, Electric). 
ELECTRIC CIRCUIT -(See Circuit, Electric). 
ELECTRIC CLOCK— (See Clock, Electric). 
ELECTRIC COIL— See Coil, Electric). 
ELECTRIC CURRENT— (See Current, Electfte). 
ELECTRIC EFFICIENCY— (See Efficiency, Electric). 
ELECTRIC ENERGY— (See Energy, Electric). 
ELECTRIC FIELD— (See Field, Electi^ Magnetic.) 
ELECTRIC FORCE— (See Force, Electric). 
ELECTRIC FURNACE— See Furnace, Electric). 
ELECTRIC FUSE— (See Fuse, Electric). 
ELECTRIC HEAT— (See Heat, Electric). 
ELECTRIC HORSl^: PO\YEPx-- (See Po^er, Horse, Electric). 
ELECTRIC INSULATION— (See Insulation, Electrio). 
ELECTRIC LAMP, ARC— (See Lamp, Electric, Arc). 

23 



ELE 346 

EI.ECTETC LAMP, INCANDESCENT— (See Lamp, Electric, 
Incandescent). 

ELECTRIC LAUNCfi— (See Launch, Electric). 

ELECTRIC LIGHT— (fsee Light, Electric). 

ELECTRIC LIGHTING, CENTRAL STATION— (See Sta- 
tion. Central). 

ELECTRIC LOCOMOTIVE— (See Locomotive, Electric). 

ELECTRIC METER— (See Meter, Electric). 

ELECTRIC MOTOR— (See Moto^, Electric). 
ELECTRIC OSCILLATIONS— (See Oscillations, Electric). 
ELECTRIC POTENTIAL— (See Potential, Electric). 
ELECl^RIC POWER— (See Pcwef, Electric). 
ELECTRIC RESISTANCE— (See Resistance, Electric). 
ELECTRIC RESONANCE— (See Resonance, Electric), 
ELECTRIC SHOClv-(See Shock, Electric). 
ELECTRIC TRAMWAY— (See Tramway, Electric). 

ELECTRIC WELDING— (See Welding, Electricj. 

ELECTRIC WHIRL- (See Whirl, Electric). 

ELECTRIC WORK -(See Work, Electric). 

ELECTRICALLY— In an electrical manner. 

ELECTRICIAN — One versed in the principles and applica- 
tions o1: electricaJ science. 

ELECTRICITY— The name given to the unknown thing, 
matter uv ^orce, or both, w^hich is the cause of electrfc 
phenomena. 

Electricity, no matter how produced, is believed to 
be one and the same thing. 



347 ELB 

ELECTRTCJTY, AM i:\rAL— Electricity produced during- life 
m the bodies of animals. 

All animals produce electricity during life. In some, 
such as the electric eel or torpedo, the amount is com- 
parativelj^ large. In others, it is small. 

ELECTRTCITV, ATMOSPHEHIC— The free electricity al- 
most always present in the atmosphere. 

ELECTEICITY, ATMOSPHERE, ORIGIN OF— The exact 
cause of the free electricity of the atmosphere is un- 
known. 

ELECTRICITY, CONTACT— Electricity produced by the 
mere contact of dissimilar metals. 

ELECTRICITY, DISTRIBUTION OF— Various combina- 
tions of electric soiirces, circuits and electro-receptive 
devices whereby electricity generated by the sources 
is carried or distributed to more or less distant electro- 
receptive devices by means of the various circuits con- 
nected therewith. 

ELECTRICITY, DISTRIBUTION OF, BY ALTERNATING 
CURRENTS— A system of electric distribution by the 
use of alternating currents. 

ELECTRICITY, DISTRIBUTION OF, BY CONSTANT CUR- 
RENTS — A S3^stem for the distribution of electricity by 
means of direct, i. e., continuous, steady or non-alter- 
nating currents, as distinguished from alternating cur- 
rents. 

ELECTRICITY, DOUBLE FLUID HYPOTHESIS OF— A 
hypothesis which endeavors to explain the causes of 
electric phenomena by the assumption of the existence 
of two different electric fluids. 



ELE 34S 

ELECTRICITY, FRICTIOXAL— Electricity produced by 

friction. 
ELECTRICITY, GALYAXIC— A term used by some in place 

of voltaic electricity. 

ELECTRICITY, HERTZ'S THEORY OF ELECTRO-MAG - 
XETIC RADIATIOXS OR WAYES— A theory, now gen- 
erally accepted, which regards light as one of the ef- 
fects of electro-magnetic pulsations or waves. 

ELECTRICITY, MAGNETO— Electricity produced by the 
motion of magnets past conductors, or of conductors 
past magnets. Electricity produced by magneto-elec- 
tric induction. 

ELECTRICITY, MULTIPLE-DISTRIBUTIOX OF, BY CON- 
STANT POTENTIAL CIRCUIT— Any system for the 
distribution of continuous currents of electricity in 
which the electro-receptive devices are connected to the 
leads in multixjle-arc or parallel. 

ELECTRICITY, NEGATI\'E— One of the phases cf electri- 
cal excitement. The kind of electric charge produced 
on resin when rubbed with cotton. 

ELECTRICITY, POSITIYE— One of the phases of electric 
excitement. I'he kind of electric charge produced on 
cotton when rubbed against resin. 

ELECTRICITY, PYRO— Electricity developed in certain 
crystalline bodies by Unequally heating or cooling them 

ELECTRICITY, SERIES DISTRIBUTION OF, BY CON- 
STANT CURRENT CIRCUIT— Any system for the dis- 
tribution of constant currents of electricity in which 
the electro-receptive devices are connected to the line- 
wire or circuit in series. 



349 ELE 

ELECTRICITY, SINGLE-FLUID HYPOTHESIS OF— A hy- 
pothesis which endeavors to explain the cause of elec- 
trical phenomena by the assumption of the existence of 
a sing-le electric fluid. 

ELECTRICITY, STATIC— A term applied to electricity pro- 
duced by friction. 

ELECTRICITY, STORAGE OF— A term improperly employ- 
ed to indicate such a storage of energj^ as will enable it 
tc directlj^ reproduce electric energy. 

ELECTRICITY, THERMO- Electricity produced by differ- 
ences of temperature at the junctions of dissimilar 
metals. 

ELECTRICITY, UNIT QUANTITY OF— The quantity of 
electricity conveyed bj' unit current per second. 

The practical unit quantity of electricity is the cou- 
lomb, v/hich is the quantity conveyed by a current of 
one ampere in one second. 

ELECTRICITY. VOLTAIC— Differences of potential pro- 
duced by the agency of a voltaic cell or battery. 

ELECTRIFICATION— The act of becoming electrified. The 
production of an electric charge. 

ELECTRIFY— To endow with electrical properties. 

ELECTROCUTION— Capital punishment by means of elec- 
tricity. 

ELECTRODE— Either of the terminals of an electric source. 

ELECTRODE, NEGATIVE— The electrode connected with 
the negative pole of an electric source. 

ELECTRODE, POSITIVE— The electrode coi^uected with 
the positive xjole of an electric source. 



ELE 350 

ELECrrwODE, SPONGE— A moistened sponge connected 
to one of the terminals of an electric source and acting* 
as the electro -therapeutic electrode. 

ELECTRODES— The terminals oi an electric source. 

ELECTRODES, CARBON, FOR ARC-LAMPS— Rods of arti- 
ficial carbon employed in arc lamps. 

These are more properly called simply arc-Jamp car- 
bons. 

ELECTRODES, CORED— Carbon electrodes of a cylindrical 
shape provided with a central cylinder of softer carbon. 

ELECTROLIER— A chandelier Tor holding electric lam^s, 
as distinguished from a chandelier for holding gas- 
lights. 

ELECTROLYSIS— Chemical decomposition effected by 
means of an electric current. 

ELECTROLYTE, TOLARIZATION OF— The formation of 
molecular groups or chains, in which the poles of all 
the molecules of any chain are turned in the same 
direction, viz: with their positive poles facing the neg'i- 
tive plate, and their negative poles facing the positive 
plate. 

ELECTROLYTIC OR ELECTROLYTICAL— Pertaining to 
electrolysis. 

ELECTROLYTIC CELL— (See Cell, Electrolytic). 

ELECTROLYTIC DECOMPOSITION— (See Decomposition. 
Electrolytic). 

ELECTR0-:NL\GNET— (See Magnet, Electro). 

ELECTRO-METALLURGY— (See !^fetallargy, Electro). 



351 ELE 

ELECTRO:NrETEH— An apparatus for measuring- differ- 
ences of potential. 

ELECTEOAfETEIi, CAPILLAKY— An electrometer in wMch 
a diSerence of potential is measured by the movemenr 
of a drop of sulphuric acid in a tube filled with mercury 

ELEClT.O^rETEK, QUADrvAT^T— An electrometer in which 
an electrostatic charge is measured by the attractive 
and repulsive force of four plates or quadrants, on a 
light needle of aluminum suspended within them. 

ELECTEOMOTIVE FORCE— (See Force, ElectromotiveJ. 

ELECTROMOTIVE FORCE, BACK OR COUNTER— (See 
Force, Electromotive, Back). 

ELECTRO PnORUS— An apparatus for the production of 
electricitj' by electrostatic induction. 

ELECTRO-PLATING— (See Plating, Electro). 

ELECTRO-PLATING BATH— (See Bath, Electro-Plating). 

ELECTROPOTON LIQUID— (See Liquid, Electropoion). 

ELECTROSCOPE— An apparatus for showing the presence 
of an electric charge, or for determining its sign, 
whether positive or negative, but not for measuring its 
amount or value. 

ELECTROSCOPE, GOLD-LEAF— An electroscope in which 
two leaves of gold are* used to detect the presence of 
an electric charge, or to determine its character wheth- 
er positive or negative. 

ELECTROSCOPE, PITH-BALL— An electroscope which 
shows the presence of a charge by the repulsion of two 
similarlj' charged pith-balls. 



ELE 352 

ELECTEOSTATIC CAPACITY— (See Caijacity, Electro- 
static). 

ELECTKOTONUS— A condition of altered functional acfiv- 
iij which occurs in a nerve when subjected to the action 
of an electric current. 

ELECTROTYPE— A type, cast or Impression of an object 
obtained by means of electro-metallurgy. (See Metal- 
lurg-y, Electro. ETectrotyping*) . 

ELECTROTYPING, OE THE ELECTROTYPE PEOCESS— 
Obtaining casts or copies of objects by depositing met- 
als in molds by the agency of electric currents. 

The molds are made of wax, or other plastic sub- 
stance, rendered conducting by coating it with po^v- 
dered plumbago. 

ELEMENT, NEGATRT:, OF A VOLTAIC CELL— That ele- 
ment or plate of a voltaic cell into which the current 
passes from the exciting fluid of the cell. The plate 
that is not acted on by the electrolyte during the gen- 
eration of current by the cell. 

ELE:MEXT, POSITTYE— That element or plate of a voltaic 
cell from which the current passes into the exciting 
fluid of the cell. The element of a voltaic couple which 
is acted on by the exciting fluid of the cell. 

ELEMENT, THEEMO-ELECTEIC— One of the two metals 
or substances which form a thermo-electric couple. 

ELEMENT, VOLTAIC— One of the two metals or sub- 
stances which form a voltaic couple. 

ELEV VTOE, ELECTEIC— An elevator operated by electric 
power. 



L 






353 ENB 

ELONOATIOX, MAGNETIC— An increase in the length of 
a bar of iron on its magnetization. 

ENDOSMOSE, ELECTRIC— Differences in the level of li- 
quids capable of mixing through the pores of a dia- 
phragm separating them, produced by the flow of on 
electric current through the liquid. 

ENERGY— The power of doing work. 

ENERGY, CONSERVATION OF— The indestructibility of 
energy. 

The total quantity of energy in the universe is un-il- 
terable. 

•ENERGY, DISSIPATION OF— The expenditure or loss of 
available energy. 

ENERGY, ELEC^nUC— The power which electricity pos- 
sesses of doing work. 

ENERGY, ELECTRIC, TRANSMISSION OF— The transmis- 
sion of mechanical energy between two distant points 
connected by an electric conductor, by converting the 
mechanical energy into electrical energy at one point, 
sending the current so produced through the conduc- 
tor, and reconverting the electrical into mechanical en- 
ergy at the other point. 

ENERGY, KINETIC— Energy which is due to motion as 
distinguished from potential energy. 

ENERGY, POTENTlAI^Stored energy. Potency, or capa- 
bility of doing work. 

Energy ]30sses??ing the power or potency of doing 
work, but not actually performing strch work. 

The capacity for doing work possessed by a body at 
rest, arising from its position as regards the earth, or 
from the position of its atoms as regards other atoms, 
with which it is capable of combining. 



EVA 354 

ENERGY, RADIANT— Energy transferred to or charged on 
the universal ether. 

ENERGY. STATIC — A term used fo express the energy- 
possessed by a body at rest, resulting from its position 
as regards other bodies in controdistinction to kinetic 
energy or tLe energy possessed by a body whose atoms, 
molecules or masses are in actual motion. 
Potential energy. 

EQUATOR, ALAGXETIC— The magnetic parallel or circle on 
the earth's surface where a magnetic needle, suspended 
so as to be /ree to m'ove in a vertical as well as a hori- 
zontal plane, remains horizontal. 

EQUIVALENT, ELECTRO-CHEMICAL— A number repre- 
senting the weight in grammes of an elementary sub- 
stance liberated during electrolysis by the pasi^age of 
one coulomb of electricity. 

EQUn^ALENT, JOULE'S— The mechanical equivalent of 
heat. 

ERG — The unit of work, or the work done when unit force 
is overcome thrrAigh unit distance. The work accom- 
plished when a body is moved through a distance of 
one centimetre with the force of one dyne. 

KTIIER — The tenuois, highly elastic lluid that is assumed 
to fill all space, and by vibrations or waves in which 
light and heat are transmitted. 

EVAPORATION, ELECTRIC— The formation of vapors at 
the surfaces of substances by the influence cf negative 
elect r if. cat ion. 



355 FAR 

EVAPOKATION, ELECTRIFICATION BY— An increase in 
the difference of potential existing-, m a niijss of vapor 
attending* its sudden condensation. 

EXCHANGE, TELEPHONIC, SYSTEM OF— A combination 
of circuits, switches and other devices, by means of 
which any one of a number of subscribers connected 
with a telephonic circuit, or a neighboring t^elephonic 
circuit or circuits, may be placed in electrical communr- 
cntion with any other subscriber connected wdth stieh 
circuit or circuits. 

EXPLODER, ELECTRIC MINE— A small mag'neto-electric 
machine used to produce the currents of high , electro- 
motive force employed in the direct firing of blasts. 

EXPLODER, ELECTRO-MAGNETIC— (See Exploder, Elec- 
tric Mine). 

EXPLORER, MAGNETIC— A smalh flat coil of insulated 
wire, used, in connection with the circuit of a tele- 
phone, to detennine the position and extent of the mag- 
netic leakage of a dynamo-electric machine ov other 
similar apparatus. 



FAPIRENHEIT'S THERMOMETER SCALE— (See Scale, 

Thermometer, Fahrenheit's). 
FALL OF POTENTIAT.— (See Potential, Fall of). 
FAN GUARD— (See Guard, Fan). 

FARAD — The practical unit of electric capacity. 

Such a capacity of a conductor or condenser that one 
coulomb of electricity is required to produce in the con- 
ductor or condenser a dijlerence of potential of one volt. 



FIB 356 

FARAD. MICRO— The millionth part of a farad. 

FAULT — ^Any failure in the proper working of a circuit 
due to ground contacts, cross-contacts or disconnec- 
tions. 

FEED, CLOCKWORK, FOR ARC LAMPS— An arrangement 
of clochwork for obtaining a uniform feed motion of 
one or both electrodes of an arc lamp. 

FEED, TO — To supplj^ with an electric current, as by a 
dynamo or other source. 

FEEDER. — One of the • conducting wires or channels 
through wh'ch the current is distributed to the main 
conductors. 

FEEDER, STANDARD OR MAIN- -The main feeder to 
which the standard pressure indicator is connected, 
and whose pressure controls the pressure at the ends 
of all the other feeders. 

FEEDERS — In a system of distribution by constant poten- 
tial, as in incandescent electric lighting, the conducting 
wires extending between the bus-wires or bars, and the 
junction boxes. 

FEET, AMPERE— The product of the current in amperes 
by the distance in feet through which that current 
passes. 

FIBRE, QUARTZ— A fibre suitable for suspending galvx- 
]:ometer needles, etc., made of quartz. 

FIBRE, VULCANIZED— A variety of insulating material 
suitable for i^arposes not requiring the highest insu- 
lation. 



357 FIE 

FIELD, AIR — '.riiat portion of a magnetic field in which 
the lines of force pass through air only, 

FIELD, ALTERNATING— An electrostatic or magnetic 
field the positive direction of the lines of force in which 
is alternately reversed or changed in direction. 

FIELD, ALTERNATING MAGNETIC— A magnetic field the 
direction of whose lines of force is alternately reversed. 

FIELD, DENSITY OF— The number of lines of force that 
pass through any field, per unit of area of cross-sectioa. 

FIELD, ELECTRO-MAGNETIC— The space traversed by the 
lines of magnetic force produced by an electro-magnet. 

FIEID, ELECTROSTATIC— The region of electrostatic in- 
fluence surrounding a charged body. 

FIELD, EXCITER OF— In a separately excited dynamo- 
electric machine, the dynamo-electric machine, voltaic 
battery, or otner electric source employed to produce 
the field of the field mag-nets. 

FIELD, INTENSITY OF— The strength of a field as meas- 
ured by the number of lines of force that pass through 
it per unit of area of cross-section. 

FIELD, MAGNETIC- -The region of magnetic influence sur- 
rounding the x>f>les of a magnet. 

A space or region traversed by lines of magnetic force. 

A place where a magnetic needle, if free to move, will 
take up a definite position, under the influence of the 
lines of magnetic force. 

FIELD, MAGNETIC, OF AN ELECTRIC CURRENT— The 
magnetic field surrounding a circuit through which an 
electric current is flowing. 

An electric current produces a magnetic field. 



FIR 358 

FIELD, MAGNETIC, PULSATORY— A field, the strength of 
which pulsates iu such manner as to produce' oscillatory 
currents by induction. 

FIELD, MAGNETIC, STRAY— That portion cf the field of 
a dynamo-electric machine which is not utilized for the 
development of differences of potential in the armature, 
because its lines of force do not pass thrcugh the arma- 
ture. 

FIELD, MAGNETIC, STRENGTH OF— The dynamic force 
acting on a free magnetic pole, placed in a magnetic 
field.^ 

FIELD, ROTATING CURRENT— A magnetic field produced 
by means ox a rotating current. 

FIGURES, MAGNETIC— A name sometimes applied to the 
groupings of iron filings on a sheet of paper so held in 
a magnetic field as to be grouped or arranged under the 
influence of the lines of force of the same. 

FILAMENT OF INCANDESCENT ELECTRIC LAMP— (See 
Lamp, Incandescent Electric, Filament of). 

FILAMENTS, FLASHED —Filaments fbr an incandescent 
lamp, that have been subjected to the flashing process, 

FINDER, RANGE, ELECTRIC— A device by means of which 
the exact distance of an enemy s snip or other target 
can be readil}^ determined. 

FIRE ALARM, AUT0:MATIC— (See Alarm, Fire, Automat- 
ic). 

FIRE ALARM SIGNAL BOX— (See Box, Fire Alarm Signal) 



359 YLV 

FIRE, HOT, ST. EL^CO'S— A term proposed by Tesla for a 
form of powerful brush discliarg-e between the second- 
ary terminals of a high frequency induction coil. 

FITTINGS OE FIXTURES, ELECTRIC LIGHT— The sock- 
ets, holders, arms, etc., required for holding or suj)port- 
ing" incandescent electric lamps. 

FIXTURES, TELEGRAPHIC— A term generally limited to 
the variously shaped supports provided for the attach- 
ment of telegraphic ^^dres. 

FLASHED FILAMENTS— (See Filaments, Flashed). 

FLASHES, AURORAL— Sudden variations in the intensity 
of the auroral light. Intermittent flashes of auroral 
light that occur during the prevalence of an aurora. 

FLASHIXC OF DYXAMO-ELECTRIC MACHINE— (See Ma 
chine, Dynamo-Electric, Flashing of). 

FLATS — A name sometimes applied to those parts of com- 
mutator segments the surface of which, through wear, 
has become lower than the other portions. 

FLOW, MAGNETIC- The magnetic flux. 

FLOW OF CURRENT, ASSUMED DIRECTION OF— (See 
Current, Assumed Direction of Flow oi*). 

FLUID, DEPOLARIZING— An electrolytic fluid in a voltaic 
cell that prevents polarization. 

FLUORESCENCE— A property possessed by certaiu solid 
or liquid substances of becoming self-luminous while 
exposed to light. 



FOH 360 

FLUX, MAG^^ETIC— The number of lines of magnetic force 
that pass or flow throug-h a magnetic circuit. The total 
number of lines of magnetic force in any magnetic field. 
The magnetic flux is also called the magnetic flow. 

FLYER, ELECTEIC— A wheel arranged so as to be set into 
rotation by the escape of convection streams from its 
points when connected with a charged conductor. 

FOCUS — A point in front or back of a lens or mirror, where 
all the rays of light meet or seem to meet. 

FOLLOWING HORX OF POLE PIECES OF DYNAMO- 
ELECTRIC MACHINE— rSee Horns, Followinff of Pole 
Pieces of a Dynamo-Electric Machine). 

FOOT-POUND— A unit of work. 

FORCE — Any cause which changes or tends to change the 
condition of rest or motion of a body. 

FORCE, CENTRIFUGAL— The force that is supposed to 
urge a rotating body directly away from the center of 
rotation. 

FORCE, COERCIVE —The power of resisting magnetization 

or demagnetization. 
FORCE, CONTACT-A difference of electrostatic potential, 

produced by the contact of dissimilar metals. 
FORCE, ELECTRIC— The force developed by electricity. 
FORCE, ELECTROMOTIVE— The force starting electricity 

in motion, or tending to start electricity in motion. 
The force which moves or tends to move electricity. 

FORCE, ELECTROMOTIVE, ABSOLUTE UNIT OF— A unit 
of electromotive force expressed in absolute or C. G. S. 
unit^. The one-hundred millionth part of a volt, since 
1 volt equals 108 C. G. S. units of electromotive force. 



361 FOR 

FORCE, ELECTROMOTIVE. AVERAGE OR MEAN— The 
sum of the \ allies of a nnmber of separate electromo^ 
tive forces divided by their number. 

FORCE, ELECTROMOTIVE, BACK— A term sometimes 
used for couuter electromotive force. 

Counter electromotive force is the preferable term. 

FORCE, ELECTROMOTIVE COUNTER— An opposed or re- 
verse electromotive force, which tends to cause a cur- 
rent in the opposite direction to that actually produced 
by the source. In an electric motor, an electrom'otive 
force contrary to that produced by the current which 
drives the motor, and which is proportional to the ve- 
locity attained by the motor. 

FORCE, ELECTROMOTIVE, DIRECT— An electromotive 
force acting- in the same direction as another electro- 
motive force already existing. 

FORCE, ELECTROMOTIVE. EFFECTIVE— The difference 
between the direct and the counter electromotive force. 

FORCE, ELECTROMOTIVE, IMPRESSED— The electromo- 
tive force acting on any circuit to produce a current 
therein. 

FORCE, ELECTROMOTIVE. INVERSE— An electromotive 
force which acts in the opposite direction to another 
electromotive force already existing. 

FORCE, ELECTROMOl IVE, OF INDUCTION— The electro- 
motive force developed by any inductive action. 

In a coil of wire undergoing induction, the value of 
the induced electromotive force does not depend in any 
manner on the nature of the material of which the coil 
is composed. 

24 



FOE 362 

FORCE, ELECTROMOTIVE, OF SECONDARY OR STOR- 
AGE CELL, TIME-FALL OF— A gradual decrease m the 
potential dii^erence of a storage battery observed dur- 
ing- the discharge of the same. 

FORCE, ELECTROMOTIVE, OF SECONDARY OR STOR- 
AGE CELL, TIME-RISE OF— A g-radual increase in the 
potential diifcrence of a secondary or storage cell ob- 
served on beg-inning the discharge after a prolonged 
rest. 

FORCE, ELECTROMOTIVE, SECONDARY IMPRESSED— 
An electromotive force produced ^vhich varies in such 
manner as to produce a simple periodic current, or an 
electromotive force the variations of which can be cor- 
rectly represented by a simple-periodic curve. 

FORCE, ELECTRO.AIOTIVE THERMO— An electromotive 
force, or difference of potential, produced by dift'erences 
cf temperature acting at thermo-electric junctions. 

FORCE, ELECTROMOTIVE VIRTUAL, OR EFFECTIVE— 
The square root of the mean square of an alternating 
or variable current. 

FORCE, ELECTROSTATIC— The force producing the at- 
tractions or repulsions of charged bodies. 

FORCE, ELECTROSTATIC, LINES OF— Lines of force pro- 
duced in the neighborhood of a charged body by the 
presence of the charge. 

Lines extending in the direction in which the force 
of electrostatic attraction or repulsion acts. 

FORCE, LINES OF, CUTTING— Passing a conductor 
through lines of magnetic force, so as to cut to inter- 
sect them. 



363 FOR 

FORCE LINES OF, DIRECTION OF— It is generally 
, agreed to consider the force lines of nuagnetic force 
as coming out of the north pole of a magnet and pas» 
ing into its south pole. 

FORCE, LOOPS OF— A term sometimes employed in the 
sense of lines of force. 

FORCE, MAGNETIC— The force which causes the attrac- 
tions cr repulsions of magnetic poles. 

FORCE, M-AGNETTC, LINES OF— Lines extending in the 
direction in which the magnetic force acts. 

Lines extending in the direction in which the force of 
magnetic attraction or repulsion acts. 

FORCE, MAGNETIC, LINES OF, CONDUCTING POWER 
FOR — A term employed by Faraday for magnetic per- 
meability. 

FORCE, MAGNETO-MOTIVE— The force that moves or 
drives the lines of magnetic force through a magnetic 
circuit against the magnetic resistance. 

FORCE, MAGNETO-MOTIVE, PRACTICAL UNIT OF— A 
value of the magneto-motive force equal to 4// multi- 
plied by the amperes of one turn, or to 1-10 of the abso- 
lute unit. 

FORCE, TUBES OF— Tubes bounded by lines of electro- 
static or magnetic force. 

FORCE, TWISTING— A term sometimes used for torque. 

FORCE, UNIT OF— A force which, acting for one second 
on a mass of one gramme, will give it a velocity of one 
centimetre per second. 

Such a force of unit is called a dyne. 



FED 364 

FOECES, PAEALLELOGEAM OF— A parallelogram con- 
structed about the two lines that represent the direc- 
tion and intensity with which two forces are simulta- 
neously acting on a body, in order to determine the 
direction and intensity of the resultant force with 
which it moves. 

FOEK, TEOLLEY— The mechanism which mechanically 
connects the trolley whee] to the trolley jjole. 

FOEMIXG PLATES OF SECOND AEY OE STOEAGE 
CELLS— rSee Plates of Secondary or Storage Cells, 
Forming* of). 

FOEMULAE — Mathematical expressions for some general 
rule, law or principle. ' 

FOUCAULT CUEEEXTS— (See Currents, Foucault). 

FEEE MAGNETIC POLE— (See Pole, Magnetic, Free). 

FEEQUENCY OF ALTEENATIONS— (See Alternations, 
Frequency of). 

FEICTIOXAL ELECTEICAL MACHINE— (See Machine, 
Frictional Electric). 

FEICTIONAL ELECTEICITY— (See Electricity, Frictional) 

FEOG, GALVANOSCOPIC- The hind legs of a recently 
killed frog employed as an electroscope or galvanoscope 
by sending an electric current from the nerves to the 
muscles. 

FEOG, TEOLLEY— The name given to the device employed 
in fastening or holding together the trolley wires at 
any point where the trolley wire branches, and prop- 
erly guiding the trolley wheel along the trolley wire on 
the movement of the car over the track. 



365 GAL 

FURNACE, ELECTRIC— A furnace in which heat gener 
ated electrically is employed for the purpose of effect^ 
ing difficult fusions for the extraction of metals froui 
their ores, or for other metallurg-ical operations. 

FL^E BLOCK— (See Block, Fuse). 

FUSE BOX— (See Box, Fuse). 

FUSE, BRANCH— A safety fuse or strip placed in a branch 
circuit. 

FUSE, CONVERTER— A safety fuse connected with the 
circuit of a converter or transformer. 

FUSE, ELECTRIC— A device for electrically igniting- a 
charge of powder. 

FUSE, MAIN — A safety fuse or strip placed in a main cir- 
cuit. 

FUSE, SAFETY— A strip, plate or bar of lead, or some 
readily fusible alloy, that automatically" breaks the cir- 
cuit in whijch it is placed on the passage of a current 
of sufficient power to fuse such strip, plate or bar, when 
such current would endanger the safety of other parts 
of the circuit. 



GAINS — The spaces cut in the faces of telegraph poles for 
the support or placing of the cross arms. 

GALVANIC BATTERY— (See Battery, Galvanic). 

GALVANIC CELL— (See Cell, Voltaic). 

GALVANIC POLARIZATION— (See Polarization, Galvanic). 



GAL 366 

GALYAXTC TASTE— (See Taste, Galvanic). 

GALVANISM — A terra sometimes employed to express the 
effects produced by voltaic electricity. 

GALVAXIZATIOX, ELECTEO-METALLUEGTCAL — The 
process of covering" any condiictive surface with a me- 
tallic coating- by electrolytic deposition, such, for ex- 
ample, as the thin copper coating- deposited on the car- 
bon pencils or electrodes used in systems of arc light- 
ing". 

GALVAXOMETER — An apparatus for measuring the 
strength of an electric current by the deflection of a 
magnetic needle. 

The galvanometer depends for its operation on the 
fact that a conductor, through which an electric cur- 
rent is flowing, will deflect a magnetic needle placed 
near it. This deflection is due to the magnetic fleld 
caused by the current. 

GALVAXO:NrETEE, ABSOLUTE— A galvanometer whose 
constant can be calculated with an absolute calibration. 

GALVAXOMETEE, ASTATIC— A galvanometer, the needle 

of which is astatic. 

GALVAXO.AfETEE, BALLISTIC— A galvanometer designed 
to measure the strength of currents that last but a mo- 
ment, such, for example, as the current caused by the 
discharge of a condenser. 

GALVAXO:\rETEE CONSTANT— (See Constant, Galvanom- 
eter). 

GALVA1S0:METEE, IJEAD-BEAT — a galvanometer, the 
needle of which comes quickly to rest, instead of swi ag- 
ing repeatedly to-and-fro. (See Damping). 



367 # GAL 

GALVANO^IETE'R, DEPREZ-D'ARSONVAL— A form of 
dead-beat galvanometer. 

GALYA>^0:METER, DIFFERET^TIAL— a galvanometer con- 
taining two coils so v^^ound as to tend to deflect the nee- 
dle in opposite directions. 

GALVANO]\rETER, FIGURE OF :MERIT OF— The recipro- 
cal of the current required to produce a deflection of 
the galvanometer needle through one degree of the 
scale. 

GALVANOMETER, MARINE— A galvanometer devised by 
Sir William. Thomson for use on steamships where the 
motion of magnetized masses of iron would seriously 
disturb the needles of ordinary instruments. 

GALVANOMETER, IStlRROR— A galvanometer in which, 
instead of reading the deflections of the needle directly 
by its movements over a graduated circle, they are read 
by the movements of a spot of light reflected from a 
mirror attached to the needle. 

GALVANOMETER, REFLECTING— A term sometimes ap- 
plied to a m.irror galvanometer. 

GALVANOMETER, SENSIBILITY OF— The readiness and 
extent to which the needle of a galvanometer responds 
to the j)assage of an electric current through its coils. 

GALVANOMETER, SINE— A galvanometer in which a ver- 
tical coil is movable around a vertical axis, so that it 
can be made to follow the magnetic needle in its deflec- 
tions. 

Tn the sine galvanometer, the coil is moved so as to 
follow the needle until it is parallel with the coil. Un- 
der these circumstances, the strength of the deflecting 
currents in any two differenf cases is proportional to 
the sines of the angles of deflection. 



GAS 368 

GALYANOMETEE, l^ANGENT— An instrument in wliich 
tlie deflecting' coil consists of a coil of wire within 
which is placed a needle very short in proportion to 
the diameter of the coil, and supported at the center 
of the coil. 

The galvanometer acts as a tangent galvanometer 
only when the needle is very small as compared with 
the diameter of the coil. The length of the needle 
should be less than one-twelfth the diameter of the coil. 

GALVANOMETEK, TORSION— A galvanometer in which 
the strength of the deflecting current is measured by 
the torsion exerted on the suspension system. 

GAP, ATE — A gap, or opening in a magnetic circuit con- 
taining air only. 

GA.P, ATE, MAGNETIC— A gap filled with air which exists 
in the opening at any part of a core cf iron or other 
m.edium of high permeability. 

GAP, SPAEK — A. gap forming part of a circuit between 
two opposing conductors, separated by air, or other 
similar dielectric which is closed by the formation of a 
spark only when a certain difference of potential is 
attained. 

G^S, DIELECTEIC, STEENGTH OF— The strain a gas is 
capable of bearing without suffering disruption, or 
without permitting a disruptive discharge to pass 
through it. 

GAS-LIGHTING, MULTIPLE ELECTEIC— A system of 
electric gas-lighting in which a number of gas-jets are 
lighted by means of a discharge of high electromotive 
force, derived from a Euhmkorff coil or a static indue- 
tfon machine. 



369 GEN 

GASSING — The evolution of gas from the plates of a stor- 
age or secondary cell. 

GAUGE, BATTEPY— A form of portable galvanometer, 
suitable for ordinary test work. 

GAUGE, WIRE, AMERICAN— A name sometimes applied 
to the Erown & Sharpe Wire Gauge. 

GAUGE, WIEE, ETEMTNGHAM— A term sometimes appliecl 
to one of the English wire gauges. 

GAUGE, WTEE. MICEOMETEE— A gauge employed for ac. 
cnrately measiiring the diameter of a wire in thou- 
sandths of an inch, based on the principle of the vernier 
or micrometer. 

GAUSS— The unit of intensity of magnetic field. 

GAi:^SS, FLEMING'S— Such a strength of magnetic field as 
is able to develop an electromotive force of one vot in 
a wire one million centimetres in length moved through 
the field with unit velocity. 

GAUSS, S. P. THOMPSON'S— Such a strength of magnetic 
field that^its intensity is equal to 108 C. G. S. units. 

GAUSS, SIE WILLIAM THOMSON'S— Such an intensity of 
magnetic field as would be produced by a current of one 
ampere at the distance of one centimetre. 

GENEEAl^OE, DYNAMO-ELECTEIC— An apparatus in 
which electricity is produced by the mechanical move- 
ment of conductors through a magnetic field so as to 
cut the lines of force. A dynamo-electric machine. 

GENEEATOE, [MOTOE— A dynamo-electric generator in 
which the power required to dri\'e the dj^namo is ob- 
tained from an electric current. 



GEA 370 

GENERATOR, PYE0-:MAGXETIC— An apparatus for pro- 
ducing- electricity directly from heat derived from the 
burning" of fuel. 

GERMAX SHAHRR ALLOY— (See Alloy, German Silver). 

GIMBA.LS- Concentric rings of brass, suspended en pivots 
in a compass box, and on which the compass card is 
supported so as to enable it to remain horizontal not- 
withstanding the movements of the ship. 

GLOBE. VAPOR, OF IXCAXDESCEXT LAMP— A glass 
globe surrounding the chamber of an incandescent elec- 
tric lamp, for the purpose of enabling the lamp to be 
safely used in an explosive atm.osphere, or to permix 
the lamp to be exposed in places where water is liable 
to fall on it. 

GOVERNOR, CITRREXT— A current regulator. A device 
' for "maintaining constant the current strength in any 
circuit. 

GOVERXOR, ELECTRIC— A device for electrically controll- 
ing the speed of a steam engine, the direction of cur- 
rent in a plating bath, the speed of an electric motor, 
the resistance of an electric circuit, the ilow of water 
or gas into or from a containing vessel, or for oiher 
similar purposes. 

GRAME— A unit of weight equal to 15.43235 grains. 

. The grame is equal to the weight of one cubic cen- 
tintetre of pure water at the temperaTure of its maxi- 
mum density. 

GRAMOPHOXE — An apx)aratus fop recording and repro- 
ducing articulate speech. 



371 -GUT 

GRAPHITE — A soft variety of carbon suitable for writing" 
on paper or similar surfaces. 

GRAY'S HARMONIC TELEGRAPHY— (wSee Telegraphy, 
Gray's Harmonic Multiple). 

GRAYITATIOX — A name applied to vhe force which causes 
masses of matter to tend to move towards one another. 

GRAYTTY, CENTRE OF— The centre of weight of a body. 

GRID — A lead plate, provided with perforations, or other 
irregularities of surface, and employed in storage cells 
for the support of the active material. The support 
provided for the active material on the plate of a sec- 
ondary or storage cell. 

GROTHUSS' HYPOTHESIS— (wSee Hypothesis, Grothuss). 

GROUND DETECTOR— (See Detector, Ground). 

GROUND OR EARTH— A general term for the earth when 
employed as a conductor, or as a large reservoir of 
electricity. ^ 

GROUND-RETURN— A general term used to indicate the 
use of the ground or earth for a part of an electric 
circuit. The earth or ground which forms part of the 
return path of an electric circuit. 

GROUND-WIRE — The wire or conductor leading to or con- 
necting with the ground or earth in a grounded circuit. 

GUARD, FAN — A wire netting placed around the f^n of an 
electric motor for the purpose of preventing its revolv- 
ing arms from striking external objects. 

GUTTA-PERCHA —A resinous gum obtained from a tropi- 
cal tree and valuable electrically for its high insulating 
powers. 



H'AE 372 

GYMNOTUS ELECTRICUS— The electric eel. 

H 

H. — A contraction for the horizontal intensity of the earth's 
magTietism. 

H. — A contraction used in mathematical writings for the 
TnagTietizing- force that exists at any point, or, gener- 
ally, for the intensitj^ of the magnetic force. 

The letter H, when used in mathematical writings or 
formulae for the intensity of the magnetic force, is 
always represented in bold or heavy faced type, thus: H 

KAIE, ELECTROLYTIC REMOVAL OF— The permanent 
removal of hair from any part of the body, by the elec- 
trolytic destruction of the hair follicles. 

HALF-SHADES FOR INCANDESCENT LAMPS—Shades 
for incandescent electric lamps, in which one-half of 
the lamp chamber proper is covered with a coating of 
silver, or other reflecting surface for reflecting the 
light, or is ground fdr the purpose of diffusing the light. 

HANDIIOLE OF CONDUIT— A box or opening commimi- 
cating with an underground cable, provided for readily 
tapping the cable, and of sufficient size to permit of the 
introduction of the hand. 

HANGER, DOUBLE-CURVE TROLLEY— A trolley hanger 
generally employed at the ends of single and double 
curves, and on intermediate points on double track 
curves, supported by lateral strain in opposite direc- 
tions. 

HANGER, TROLLEY— A device for supporting and prop- 
erly insulating trolley wires. 

HARMONIC RECEIVER— (See Receiver, Harmonic). 



373 HEA 

HARMONIC TELEGEAPH— (See Telegraphy, Gray's Har- 
monic Multiple). • 
HEAD LIGHT, LOCOMOTIVE, ELECTRIC— An electric 
light placed in the focus of a parbolic reflector in front 
of a locomotive engine. 

The lamp is so placed that its voltaic arc is a little 
out oi the focus of the reflector, so that, by giving a 
slight divergence to the reflected light, the illumination 
extends a short distance on either side, of the tracks. 
HEAT— A form of energy. 

The phenomena of heat are due to a vibratory motion 
impressed on the molecules. Heat is transmitted 
through space by means of a wave motion in the univer- 
sal ether. This wave motion is the same as that caus- 
ing light. 

A hot body loses its heat by producing a wave mo- 
tion in the surrounding ether. This process is called 
radiation. (See Radiation). 

The energy given off by a heated body cooling is 
called radiant energy. 
HEAT ELECTRIC— Heat produced by means of electric 

current. 
HEAT, MECHANICAL EQUIVALENT OF— The amount of 
mechanical energy, converted into heat, that would be 
required to raise the temperature of 1 pound of water 1 
degree Fahr. 

The mechanical equivalence between the amount of 
energy expended and the amount of heat produced, as 
measured in heat units. 

Rowland's experiments, the results of which are gen- 
erally accepted, gave 778 foot-pounds as the energy 
equivalent to that expended in raising the temperature 
of 1 pound of water from 39 degrees F. to 40 degrees F. 



BEN 



374 



HE VT SPECIFIC The capacity of a substance for heat as 

compared with the capacity of an eqnal quantity of 
some other substance taken as unity. 

Water is o-enerally taken as the standard for compari- 
son, because its capacity for heat is greater than that 
of any other common substance. 

HEAT UNIT— The quantity of heat required to raise a 
given weight of water through a single degree. 

(1.) The British Heat Unit, or Thermal Unit, or 
the amCTint of heat required to raise 1 poimd of water 
at greatest density 1 degree Eahr. This unit represents 
an amount of work equal to 778 foot-pounds. 

(2.) The Greater Calorie, or the amount of heat re- 
quired to raise the temperature of 1,000 grames of 
water 1 degree C ^See Calorie). 

(3.) The Smaller Calorie, or the amount of heat re- 
quired to raise the temperature 1 gramme of water 1 
degree C. 

(4.) The Joule, or the quantity of heat developed in 
one second by the passage of a current of one ampere 
through a resistance of one ohm. 

HEATEE.ELECTRIC— A device for the conversion of elec- 
tricity into heat for purposes of artificial heating. 

HEDGEHOG TEANSFOKMEK— (See Transformer, Hedge- 
hog). 

HENKY, ^— The practical unit of self-induction. 

A circuit has a self-induction of one Henry when a 
change of one ampere per second produces in it a coun- 
ter E. M. F. of one volt. 



375 HOR 

HIGH-BARS — A term applied to those commutator seg"- 
ments, or part? of commutator segments, which, 
throug-h less wear, faulty construction or looseness, are 
hii^her than adjoining' portions. 

HOLDERS, CARBON, FOR ARC LAMPS— A clutch or clamp 
attached to the end of the lamp rod or other support, 
and provided to hold the carbon pencils used on arc 
lamps. 

HOLDERS FOR BRUSHES OF DYXAMO-ELECTRIC MA- 
CHINE — A device for holding* the collecting brushes of 
a dynamo-electric machine. 

HOLTZ MACHINE— (See Machine, Holtz). 

HOOD FOR ELECTRIC LA:\[P— A hood provided for the 
double purpose of protecting the body of an electric 
lamp from rain or sun, and for throwing Its light in a 
general downward direction. 

HORIZONTAL COMPONENT OF EAR I^H'S :NL4GNETIS]Nr— 

(See Component, Horizontal, of Earth's Magnetism). 

HORNS, FOLLOWING, OF POLE PIECES OF A DYNAMO- 
ELECTRIC MACHINE— The edges or terminals of the 
pole pieces of a dynamo-electrical machine from which, 
the armature is carried during its rotation. 

HORNS, LEADING, OF POLE PIECES OF A DYNA:M0- 
ELECTRTC MACHINE— The edges or terminals of the 
pole pieces of a dynamo-electrical machine from which 
the armature is carried during its rotation, 

HORSE-POWER— A commercial unit for power or rate of 
doing work. 

HORSE-POWER, ELECTRIC— (See Power, Horse, Electric). 



HYS 376 

HOESESHOE MAGNET— (See Magnet, Horseshoe). 
HOTEL ANNUNCIATOFv— (See Annunciator, Hotel). 

HOUE, AMPEEE— A unit of electrical quantity equal to 
one ampere flowing for one hour. 

HOUE, HOESE-POWEE— A unit of work. 

An amount of work equal to one-horse power for an 
hour. 

One horse power is equal to 1,980.000 foot-pounds, or 
745.941 "watt hours. 

HOUE, KILO-WATT— A unit of electrical power equal to 
a kilo-watt maintained for one hour. 

HOUE, LAMP — Such a service of electric current as will 
maintain one electric lamp during one hour. 

HOUE, WATT— A unit of electrical work. 

An exjDenditure of electrical work of one watt for 
one hour. 

HUMAN BODY, ELECTEICAL EESISTANCE OF-(See 
Body, Human, Eesistance of). 

HYDEOGEN, ELECTEOLYTIC— Hydrogen produced by 
electrolytic decomposition. 

HYPOTHESIS, GEOTIIUSS— A hjrpothesis produced by 
GrothiTSS to account for the electrolytic phenomena 
that occur on closing the circuit of a voltaic cell. 

HYSTEEESIS— Molecular friction to magnetic change of 
stress. 

A retardation of the magnetizing or demagnetizing 
effects as regards the causes which produce them. 

The quality of a paramagnetic su,bstance by virtue of 
which energy is dissipated on the reversal of its mag- 
netization. 



377 j^Q 

r 

I. H. P. — A contraction for indicated horse-power, or the 
horse-power of an engine as obtained by the means of 
an indicator card. 

IGNITION, ELECTRIC— The ignition of a combustible ma- 
terial by heat of an electric origin. 

ILLUMINATION, ARTIFICIAL— The employment of artifi- 
cial sources of light. 

ILLUMINATION, UNIT OF— A standard of illumination 
proposed oy Preece, equal to the illumination given by 
a standard candle at the distance of 12.7 inches 

IMPEDANCE— Generally any opposition to current flow. 

A quantity which is related to the strength of the 
impressed electromotive force of a simple periodic or 
alternating current, in the same manner that resistance 
is related to the siteady electromotive force of a con- 
tinuous current. 

IMPEDANCE COIIr-(See Coil, Imipedance). 

IMPRESSED FLECTROMOTIVB FORCE— (See Force, Elec- 
troanotive, Impressed). 

INCANDESCE— To shine or glow by means of heat. 

INCANDESCENCE, ELECTRIC— The shining or glowing of 
a substamce, generally a solid, by means of heat of elec- 
tric origin. 

INCLINATION, ANGLE OF— The angle which a magnetic 
needle, free to move im a horizontal plane, makes wit a 
a horizontal line passing through its^point of support. 
The angle of magnetic dip. 

25 



IND 378 

IXiCAXDESCENT ELECTEIC T^\]MP— (See r>amp, Electric, 
Incandescent). 

IXCLIXATIOX, MAGXBTIC— The angular deviation from 
a horizontal position of a freely suspended magnetic 
needle. 

IXDIA EUBBEE — A resinous substance obtained from the 
milky juice of several tropical trees. 

IXDIOATOE, ELECTEIC— A name applied to various de- 
vices, generally operated by the deflection af a mag- 
netic needle, or the ringing of a bell, or both, for indi- 
cating, at some distant point, the condition of an elec- 
tric circuit, the 'Strength of current thaif is passing 
through it, the height of water or oth'er liquid, the 
p«ressure o'a a boiler, the tennperature, the speed of an 
engine or line of shafting, the working of a machine or 
other similar events or occurrences. 

IXDICATOE, ELBCTEIC, FOE STEAMSHIPS— An electric 
indicator operated by circuits connected with the throt- 
tle valve and reversing gear of the stea«m engine. 

IXDICATOE, LAMP— An apparatus used in the central sta- 
tion of a system of incandescent lamp distribution to 
indicate the presence o-f the proper voltage or potential 
•difference en the mains. 

IXDICATOE, POTEXTIAL— An apparatus for indicating 
the potential diffeience between any points of a circuit. 

IXDICATOE, SPEED— A name sometimes applied to a 
tachcgneter. A revolution counter. 

INDUCED CrEEEXT~(See Current, Induced). 



379 IND 

INDUCTAiSrCE— The induction of a current on itself, or od 
other circuits. 

Self-induction. 

A term generally employed instead of self-induction. 

That property in virtue of which a finite electromo- 
tive force, acting on a circuit, does not im^mediately 
generate the full current due to its resistance, 'and 
when the electromotive force is withdrawn, time is re- 
quired for the current sitrength to fall to zero. — (Flem- 
ing.) 

A quality by \^rtue of which the passage of an elec- 
tric current is necessarily accomipanied by the absorp- 
tion of electric energy in the formation of a magnetic 
field. 

INDUCTANCE, CO-EFFICIENT OF— A constant quantity, 
such that when multiplied hy the current strength 
passing in any coil or circuit, "vvill represent numerlcal- 
1}' the induction through the coil or circuit due 'to that 
current. 

A term sometimes used for co-efficient of self-induc- 
tion. 

INDUCTANCE, VARIABLE— The inductance .which occui-. 
in circuits formed partly or wholly of substances like 
iron or other paramagnetic substances, the magnetic 
permeability of which varies with the intenisity oif the 
magnetic induction, and where the lines of force have 
their circuit partly or wholly in soich material or vari- 
able magnetic peroneability. 

INDUCTION — An infiuence exertea by a charged body or 
by a magnetic field on neighboring bodies without ap- 
parent communication. 



IIN-U 380 

INDUCTIOX, ELBGTEO— DYNAMIC— Electromotive forces 
set up by induction in conductors which are either ac- 
tually or practically moved so as to cut the lines of 
magnetic force. 

These electramo-tive forces, when permitted to act 
through a circuit, produce an eleciric current. 

I1SDUCTI0X, ELBCTRO-MAGXETIC— .A variety of electro- 
dynamic induction in which electric currents are pro- 
duced by the motion of electro-magnetic solenoids. 

INDUCTION, ELECTEOSTATIC— The production of an 
electric charge in a. conductor brought inito an electro- 
static field. 

INDUCTION, MAGNETIC— The pi:oduction of magnetism 
in a magnetizable subs»tance by bringing it into a mag- 
netic field. 

INDUCTION, MAGNETIC, CO-EFFICIENT OF— A term 
sometimes used instead of magnetic permeability. 
(See Permeabilit}', Magnetic). 

INDUCTION, MAGNETIC LINES OF— Lines which show 

* 

not only the direction in which magnetic induction 
takes place, but also the magnitude af the induction. 
This term is often loosely used for lines of force. 

INDUCTION, MAGNETIC-ELECTEIC— A variety of electro- 
djmamic induction in which electric currents are pro- 
duced by the motion of permanent magnets, or of con- 
ductors past permanent magnets. 

INDUCTION, MUTUAL— Induction produced by two neigh- 
boring circuits on each other by the mutual interaction 
of their magnetic fields. 



381 iNr> 

INDUCTION, MUTUAL, CC-EFFICIENT OF— The quanti- 
ty which represents the numiber of lines of force which 
are common to or linked in with 'tw^o circuits, which are 
producing mutual induction on each other. 

INDUCTION, REFLECTION OF— A term proposed by 
Fleming" to express an action which resembles a reflec- 
tion of inductive power. 

INDUCTION, SELF— Induction produced in a circuit while 
changing- the current therein iby the induction o-f the 
current on itself. 

INDUCTION, SELF, CO-EFFICIENT OF— The amount of 
cutting of magnetic lines in any circuit due to the pas- 
sage of unit current. 

For a given coil the co-efficient of self-induction 
is, according to S. P. Thompson: 

(1.) Proportional to the square of the number of 
convolutions. 

(2.) Is increased by the use of an iron core. 
(3.) If the magnetic permeability is assumed as con- 
stant, the co-efficient of self-induction is numerically 
equal to the product of the number of lines of magnetic 
force due to the current, and the number of times they 
are enclosed by the circuit. 

INDUCTION, TOTAL INIAGNETIC— The total magnetic in- 
duction of any space is the number of lines of magnetic 
induction w^liich pass through that space, where the 
magnetizable material is placed together with the lines 
added by the magnetization of the magnetic material. 

INDUCTION, UNIPOLAIl— A term sometimes applied to 
the induction that occurs when a conductor is fjo 
moved through a magnetic field as to continuously cut- 
its lines of force. 



INK 382 

IXDUCTIOiXLESS RESISTAXCE— (See Resistance, Induc- 
tionless.) 

INDUCTIVE CAPACITY, SPECIFIC— (See Capacit3% Speci- 
fic Inductive.) 

INDUCTIVE CIRCUIT— (See Circuit, Inductive.) 

INDUCTIVE RESISTANCE— (See Resistance, Inductive.) 

INDUCTOR DYNAISEO— (See Dynamo, Inductor.) 

INDUCTORIUM— A name sometimes applied to a Ruhm- 
korff induction coil: 

INEQUALITY, ANNUAL, OF EARTH'S MAGNETISM - 
Variations in the value of the earth's magnetism dur- 
ing' the earth's revolution depending on the position 
of the sun. 

Annual variations in the earth's magnetism. 

INERTIA— The inability of a body to change its condition 
of rest or motion, unless some force acts on it. 

INERTIA, ELECTRIC — A term sometimes employed in- 
stead of electro-magnetic inertia. 

A term employed to indicate the tendency of a cur- 
rent to resist its stopping or starting. 

INERTIA, ]MAGNETIC— The inability of a magnetic core 
to instantly lose or acquire magnetism. 

INFLUENCE, :\LACHINE— (See Machine, Electrostatic In- 
duction.) 

INK WRITER, TELEGRAPHIC— A device employed for 
recording the dots and dashes of a telegraphic message 
in ink on a fillet or strip of paper. 



383 INT 

INSTALLATION — A term embracing the entire plant and 
its accessories required to perform any specified work. 
The act of placing, arranging- or erecting a plant or 
apparatus. 

INSTALLATION, ELECTRIC— The establishment of any 

electric plant. 
INSULATING STOOL— (See Stool, Insulating.) 

INSULATING TAPE— (See Tape, Insulating.) 

INSLT:.ATT0N; electric— Non-conducting material so 
placed vnih respect to a conductor as to prevent the 
loss of a charge, or the leakage of a current. 

INSULATOR, DOUBLE-CUP— An insulator consisting of 
two funnel-shaped cups, placed in an inverted position 
on the supporting pin and insulated from one another 
by a free air space, except near the ends, which are 
cemented. 

INSLILATOR, FLUTD- An insulator provided with a small, 
internally placed, annular, cup-shaped space, filled with 
an insulating oil, thus increasing the insulating power 
of the support. 

INSULATOR, OIL— A fluid insulator filled with oil. 

INSULATOR TELEGRAPHIC OR TELEPHONIC— A non- 
conducting support of telegraphic, telephonic, electric 
light or other wires. 

INTENSITY, MAGNETIC— Density of magnetic induction. 
INTENSITY OF CURRENT— (See Current, Intensity of.) 
INTENSITY OF FIELD— (See Field, Intensity of.) 
INTENSITY OF MAGNETIZATION— (See Magnetization, 
Intensity of.) 



ISO 384 

IXTBXSITY, PHOTOMETRIC, UXIT OF— (The amount of 
light produced by a candle that- consumes two grains 
of spermaceti wax per minute.) 

INTEERUPTER, AUTOMATIC— An automatic contact 
breaker. 

INTERRUPTER, TUNIXG-FORK— An interrupter in which 
the successive makes and breaks are produced by the 
vibrations of a tuning-fork or reed. 

INVERSION, THERMO-ELECTRIC— An inversion of the 
thermo-electric electromotive force of a couple at cer- 
tain temperatures. 

IONS — Groups of atoms or radicals which result from the 
electrolytic decomposition of a molecule. 

TONS, ELECTRO-NEGATIVE— The negative atoms, or 
groups of atoms, called radicals, into which the mole- 
cules of an electrolyte are decomposed by electrolysis. 

IONS. ELECTRO-POSITIVE—The positive atoms, or groups 
of atoms, called radicals, into which the molecules of 
an electrolyte are decomposed by electrolysis. 

IRON-CLAD ELECTRO-MAGNET— (See Magnet, Electro, 
Iron-Clad.) 

IRON CORE, EFFECT OF, ON THE MAGNETIC 
STRENGTH OF A HOLLOW COIL OF WIRE— An iu- 
crease in the number of lines of magnetic force, be- 
yond those produced by the current itself, due to the 
opening out of the closed magnetic circuits in the atoms 
or molecules of the iron. 

ISOCHRONIS^Nl— Equality of time of vibration or motion. 
A contraction proposed for Joule. 



C85 JOI 



JABLOCHKOFF CAXDLE— (See Candle, Jablochkoff.) 

JAR, LEYDEN — A condenser in the form of a jar, in 
which the metallic coatings are placed opposite each 
other on the outside and the inside of the jar respec- 
tively. 

JAR, LEYDEN, CAPACITY OF— The quantity of electricity 
a Leyden jar will hold at a g-iven difference of poten- 
tial. 

JAR, LIGHTNING— A Leydon jar, the coatings of which 
consist of metallic filling's. 

As the discharge passes, an irregular series of sparks 
appear, which somewhat resemble in their shape a 
lightning flash. Hence the origin of the term. 

JAR OF SECONDARY CELL— The containing vessel in 
which ^he plates of a single secondary cell arc placed. 

JAR, POROUS— A porous cell. 

JAR,UNrT— -A small Leyden jar sf»metimes employed to 
measure approximately the quantity of electricity 
passed into a Leyden battery or condenser. 

JOINT, .-\MERTCAN TWIST— A telegraphic or telephoni • 
joint in which each of the two wires is twisted around 
the other. 

JOINT. P.RITANNIA — A telegraphic or telephonic joint in 
which the wires are laid side by side, bound together 
and subsequentlj" soldered. 

JOINT, MAGNETIC— The line of junction between two 
separate parts of magnetization material. 



KEK 386 

JOINT, SLEEVE — A junction of the ends of conducting 
wires obtained by passing them through tabes and 
then twisting and soldering. 

JOINT, TESTING OF— Ascertaining the resistance of the 
insulating material around a joint in a cable. 
A contraction for electrostatic capacity. 

JOULE — TJie unit of electric energy or work. 
1 joule equals .73732 loot-pounds. 
1 joule per second equals 1 watt. 

The British Association proposed to call one joule 
the work done by one watt in one second. 

K 

K. W. — A contraction for kilo-watt. 

KAOLIN — A variety of white clay sometimes employed for 
insulating pui-poses. 

KAPP LINES— (See Lines, Kapp.) 

KAETAYERT— A kind of insulating material resembling 
fiber. 

KATHION — The electro-positive ion, atom or radical into 
which the molecules of an electroh'te is decomposed 
iby electrolysis. 

KATHODAL— Pertaining to the kathode. 

KATHODE — The conductor or plate of an elect- o-decom- 
position cell connected with the negative terminal or 
electrode of a battery or other source. 

KEEPER OF MAGNET— (See Magnet, Keeper of.) 

KERITE — An insulating material. 



387 KIL 

KEY, DISCHARGE— A key employed to enable the dis- 
charge from a condenser or cable to be readily passed 
through a galvanometer for purposes oi measure- 
ment. 

KEY, IXCEEMEXT, OF QUADRUPLEX TELEGRAPHIC 
SYSTEiM — A key employed to increase the strength of 
the current and so operate one of the dlistant instru- 
ments in a quadruplex sj^stem by an increase in the 
streng^th of the current. 

KEY PLUG — A simple form of key in which a connection 
is readily made or broken by the insertion of a pkig' of 
metal between two metallic plates that are thus in- 
troduced into a circuit. 

KEY, RBVBRSIXG— A key inserted in the circuit of a gaL 
vanometer for obtaining deflections of the needle on 
either side of the galvanometer scale. 

KEY, REYERSIXG, OF QUADRUPLEX TELEGRAPHIC 
SYSTEM — A key employed to reverse the direction of 
the current and so operate one of the distant instru- 
ments, in a quadruplex system, by a chauige in the di- 
rection of the current. 

KEY, SHORT-CIRCUIT— A key which in its normal condi- 
tion short circuits galvanometer. 

KEY, TELEGRAPHIC- The key employed for sending over 
the line the successive makes and breaks that product- 
the dots and dashes of the Morse alphabet, or the de- 
flections of the needle of the needle telegraph. 

KICKIXG COIL— (See Coil, Kicking.) 

KILOAMPERE— One thousand amperes. 

KILOGRAMME— One thousand grammes, or 2.2046 pounds 
avoirdupois. 



LAG S88 

KILOWATT— One thousand -^vatts. 

KILOWATT HOUR— (See Hour, Kilowatt.) 

KIXETIC ENERGY— (See Energ-y, Kinetic.) 

KINETOGRAPH — A device for the simultaneous reproduc- 
tion of a distant stage and its actors under circum- 
stances such that the actors can be heard at any dis- 
tance from the theatre. 

KITE, FRAXKLIX'S— A kite raised in Philadelphia, Pa., 
in June, 1752, by means of T\'hich Franklin experiment- 
ally demonstrated the identity between lightning* an«.l 
electricity, and which, therefore, led to the invention 
of the lightning rod. 

KNIFE, BREAK SWITCH— (See Switch, Knife Break.) 



L — A contraction for co-efficient of inductance. 

L — A contraction for length. 

LAG, ANGLE OF— The angle through which the axis of 
mas-netism of the armature of a dvnamo-electric ma- 
chine is shifted by reason of the resistance its core 
offers to sudden reversals of magnetization. 

LAG, ANGLE OF, OF CURRENT— An .angle (whose ta^igent 
is equal to the ratio of the inductive to the ohmic re- 
sistance. 

An angle, the tangent of which is equal to the induc- 
tive resistance of the circuit, divided by the ohmic re- 
sistance of the circuit. 

LAG, MAGNETIC--A magnetic viscosity as manifested by 
the sluggishness with which a magnetizing force pro- 
duces its magnetizing effects in iron. 



389 LAM 

LAMINATE© CORE— (See Core, Lamicaled.) 

LAMP, ALL-XIGHT — A term sometimes applied to a 
double-canbon arc lamp. 

LAMP, AEC, ELECTRIC— An electric lamp in which the 
light is produced by a voltaic arc formed between two 
or more car'bon electrodes. 

LAMP, CHAMBER OF— The glass bulb or chamiber of an 
incandescing electric lam-p in which the incandescing 
conductor is placed, and in w^hich is maintained a high 
vacuum. 

LAMP, ELECTRIC, ARC, DIFFERENTIAL— An arc lamp 
in 'Which the movements of the carbons are controlled 
by the differential action of two magnets opposed to 
each other, one of whose coils is in the direct 'and the 
other in shunt circujit around the carbons. 

LAMP, ELECTRIC, ARC, DOUBLE CARBON— An electric 
arc lamp provided with two pairs of carbon electrodes, 
so arranged that ^vhen one pair is consumed, the cir- 
cuit is automatically completed through the other pair. 

LAMP, ELECTRIC GLOW— A term employed mainly in 
Europe for an incandescent electric lamj). 

LAMP, ELECTRIC, INCANDESCENT— An electric lamp in 
which the light is produced by the electric Incandes- 
cence of a strip or filament of some refractory sub- 
stance, generally carbon. 

LAMP, ELECTRIC, INCANDIZSCENT, LIFE OF— The num- 
ber of hours that an incandescent electric lamp, when 
traversed by the normal current, will continue to af- 
ford a sfooci commercial lig'lit. 



LAW 390 

LAMP, ELECTEIC, SAFETY— An incrindesoent electnc 
lamp, wth thoroughlv insulated leads, employed in 
mines, or other similar places, where the exjjlosive ef- 
fects of readily ignitable substances are to be fear?d. 

LAMP, ELECTRIC, SERIES CONNECTED INCANDES- 
CENT — An incandescent electric lamp adapted for use 
in series circuits. 

LAMP, ELECTRIC, INCANDESCENT, ELECTRIC FILA- 
MENT OF — A term now generally applied to the in- 
candescing conductor of an incandescent electric 
lamp, whether the same be of very small cross-section 
or of comparatively large cross-section. 

LAMP, PILOT — In systems for the operation of electric 
lamps, an incandescent lamp emplpj^ed in a station 
to indicate the difference of potenial at the dynamo 
terminals, bj^ means of the intensity of its emitted 
light. 

LAMP ROD— (See Rod, Lamp.) 

LAMPS, BANK OF— A term applied to a number of lamps, 
equal to about half the load, that were formerly 
placed in view of the attendant in circuit \vith a dyna- 
mo that is to be placed in a parallel circuit with 
another dynamo, one of the lamps of which is also in 
view. 

LAMPS, CARBONTNG—Placing carbons in electric arc 
lamps. 

LAUNCH, ELECTRIC— A boat, the motive power for which 
is electricity, suitable for launching from a ship. 

LAW, JACOBI'S— The maximum work done by a motor is 
reached when the counter-electromotive force is equal 
to one-half of the impres<^ed electromotive force. 



391 LAW 

LAW. JOULE'S — The heating- power of a current is pro- 
portional to the product of the resistance and the 
square of the current strength. 

LAW, NATURAL — A correct expression of the order in 
which the causes and elfects of natural phenomena fol- 
low one another. 

LAW OF OHM, OTJ LAW OF CURRENT STRENGTH- -The 
strength of a continuous current is directly propor- 
tional to the dilference of potential or electromotive 
force in the circuit, and inversely proportional to the 
resistance of the circuit, i. e., is equal to the quotient 
arising- from dividing- the electromotive force by the 
resisftance. 

LAW, YOLTAMERIC— The chemical action produced by 
electrolysis in any electrolyte is proportional to the 
amount of electricity which pasf^es through the elec- 
trolyte. 

LAWS, LENZ S — Laws for determining the directions of 
currents produced by electrodynamic induction. 

The direction of the currents set up by electrodyna- 
mic induction is always such as to oppose the motions 
by whch such currents were produced. 

LAWS OF COULOMB, OR LAWS OF ELECTROSTATIC 
AND MAGNETIC ATTRACTIONS AND REPULSIONS. 
— I^aws for the force of attraction and repulsion be- 
tween charged bodies or between magnet poles. 

Tlie fact that the force of electrostatic attraction or 
repulsion between two charges, is directly proportional 
to the product of the qualities of electricity of the two 
charges and inversely proportional to the square of the 
distance between them, is known as Coulomb's Lonv. 



LEG 392 

LAWS 01 JOULE — La^vs expressing the (le^elopnient ol 
heat produced in a circuit by an electric current. 

LEAD, AXGLE OF— The angular deviation from the nor- 
mal position, which must be given to the collecting- 
brushes on tlie commutator cylinder of a dynamo-elec- 
tric ujachine, in order to avoid destrucr/ive burning. 

LEAD OF BRUSHES OF DYXA^^LO-ELEC'l'lJlC MACHl^JE 
— Tiie angular deviation from the normal position, 
■which it is necessary to give ihe brushes on Ihe com- 
mutator of a dynamo-elect tic nia chine, iji order to ob- 
tain t fTicient action. . 

LEADING TIOl^X OF POLE PIECES OF DYNA?10-ELEC- 
TEIC MACIITXE— (See Horns, Leading, of Pole Pieces 
of a Dynamo-Electric ^lachine). 

LEADIXG-IX WIKES— (See Wires, Leading-In). 

LEx\DS — The conductors in any system of electric distribu- 
tion. 

LEAKAGE, ELECTKIC— The gradual dissipation of a cur- 
rent due to insufficient insulation. 

LEAKAGE. MAGXEjl...— A useless dissipation of the lines 
of magnetic force of a dynamo-electric machine, or 
other similar device, by their failure to pass through 
the armature where they are needed. 

Useless dissipation of ]ines of magnetic force outside 
* that portion of the field of a dynamo-electric machine 
through which the armature moves. 

LECLAXCHE'S VOLTAIC CELL— (See Cell, Voltaic, Le- 
clanche). 



393 L.IG 

LEG — In a system of telephonic exchange, where a ground 
return is used, a single wire, or, where a metallic cir- 
cuit is employed, two wdres, for connecting a subscriber 
with the niain switchboard, by means ot which any 
sub??criber may be legged or placed directly in circuit 
with two or more other parties. 

LEGAL OHM— (See Ohm, Legal). 

LENGTH OF SPAEK— (See Spark, Length of). 

LENZ'S LAW— (See Law, Lenz's). 

LEYDEN JAR Bx^TTERY— (See Battery, Leyden Jar). 

LIGHT, ELECTRIC— Light produced hy the action of elec- 
tric energy, 

LIGHT, MA.X WELL'S, ELETRO-MAGNETIC THEORY OF 
- — A hypothesis for the cause of light produced by Max-- 
w^ell, based on the relations existing between the phe- 
nomena of light and those of electro-magnetism. 

LIGHT, SEARCH, ELECTRIC~An electric arc light placed 
in a focusing lamp before a lens or mirror, so as to ob- 
tain either a parallel beam or a slightly divergent pen- 
cil of light for lighting the surrounding space for pur- 
poses of exploration. 

LIGHTER, CIGAR, ELECTRIC— An apparatus for electric- 
ally lighting a cigar. 

LIGHTING, ARC— Artificial illumination obtained by 
means of an arc light. 

The term arc lighting is used in contradistinction to 
incandescent lighting. 

LIGHTING, ELECl^RIC, CENTRAL STATION— The light- 
ing of a number of houses or other buildings from a 
single station, centrally located. 

26 



LIG 394 

LIGHTING, ELECTKIC GAS— Igniting gas jets by means 
of electric discharges. 

LIGHTING, ELFXTRIC, ISOLATED— A system of electric 
lightipg where a separate electric source is placed in 
each house or area to be lighted, as distinguished from 
the central station lighting, where electric sources are 
provided for the production of the current required for 
an entire neighborhood. 

LIGHTNING— The spark or bolt that results from the dis- 
ruptive discharge of a cloud to the earth, or to a neigh- 
boring cloud. 

LIGHTNING AEKESTER— (See Arrester, Lightning). 

LIGHTNING, BACK-STROKE OF— An electric discharge, 
caused by an induced charge, which occurs after the 
direct discharge of a lightning fiash. 

LIGHTNING, CHAIN— A variety of lightning flash in which 
the discharge takes a rippling path, somewhat resem- 
bling a chain. 

LIGHTNING, FORKED— A variety of lightning flash, in 
which the discharge, on nearing the earth or other 
object, divides into two or more branches. 

LIGHTNING, GLOBULAR— A rare form of lightning, in 
which a. globe of Are appears, which quietly floats for a 
while in the air and then explodes with 'great violence. 

LIGHTNING, HEAT— A variety of lightning flash in which 
the discharge lights up the surfaces of tTie neighboring 
clouds. 

LIGHTNING, SHEET— A variety of lightning flash unac- 
companied by any thunder audible to the observer, in 
which the entire surfaces of the clouds are illuminated. 



I 



395 LIN 

^T^rHTNING, VOLCANIC— The lightning discharges that 
attend most volcanic eruptions. 

LIGHTNING, ZIGZx\G— The commonest variety of light- 
ning flashes, in which the discharge apparently as- 
sumes a forked zigzag, or even a chain-shaped path. 

LINE-— A wire or other conductor connecting any two 
points or 5?tations. 

LIXE, AERIAL — An air line as distinguished from an un- 
derOTOund conductor. 

LINE, AKTIFICIAL — ^A line so made up by condensers and 
resistance coils as to have the same inductive eHects 
on charging or discharging as an actual telegraph line. 

LINE, CAPACITY OF— The ability of a line or cable to act 
like a condenser, and therefore like it to possess a ca- 
pacity. 

LIXE CIRCUIT— (See Circuit, Line). 

LINE, NEUTRAL, OF A :MAGNET— A line joining the neu- 
tral points of a magnet or points approximately mid- 
way between the poles. 

LINE, NEUTR.VL, OF COMMUTATOR CYLINDER— A line 
on the commutator cylinder of a dynamo-electric ma- 
chine connecting the neutral points, or the points of 
maximum positive and negative difference of potential. 

LIXEMAN — One who puts up and repairs line circuits and 
attends to the devices connected therewith. 

LTXES, KAPP— A term proposed by Mr. Gisbert Kapp for 
a unit of lines of magnetic force. 
One Kapp lire equals 6,000 C, G. S. magnetic lines. 



LOG 396 

LINES OF FOPiCE, CUTTING— (See Force, Lines of, Cat- 
ting). 

LINES OF FOPvCE, DIRECTION OF— (See Force, Lines of, 
Direction of). 

LINES OF MAGNETIC FORCE— (See Force, Magnetic, 
Lines of). ' 

LINES, OVERHEAD— A term applied to telegraph, tele- 
phone and electric light or power lines that run over- 
head, in contradistinction to similar lines placed un- 
derground, 

LINKS, FUSE — Strips or plates of fusible metal in the form 
of links, employed for safety fuses for incandescent or 
other circuits. 

LIQUID, ELECTROPOION— A battery liquid consisting oi 
1 pound of bichromate of potash dissolved in 10 pounds 
of water, to which 2% pounds of commercial sulphuric 
acid has been gradually added. 

LIQUID, EXCIXTNG, OF VOLTAIC CELL The electro- 

lyte or liquid in a voltaic cell, which acts on the posi- 
tive plate. 

LOAD, LIQUID RESISTANCE— An artificial load for^ a 
dynamo-electric machine, consisting of a mass of liquid 
interposed between electrodes. 

LOCAL BATTERY— (See Battery, Local). 

LOCOMOTIVE, ELECTRIC— A railway engine whose mo- 
tive power is electricity. 

LOCOMOTIVE HEAD LIGHT, ELECTRTC-(See Head 
Light, Locomotive), 



397 MAO 

LODESTONE— A name formerly applied to an ore or iron 

(magnetic iron ore), that naturally possesses the power 
of attracting pieces of iron to it. 

LOOP, ELECTEIC — A portion of a main circuit consisting- 
of a wire going out from one side of a break in the 
main circuit and returning to the other side of the 
break. 

M 

MACHINE, AEMSTEONG'S HYDRO-ELECTKIC— A ma- 
chine for the development of electricity by the friction 
of a jet of steam passing over a water surface. 

MxiCHIXE, DYXAMO-ELECTEIC— A machine for the con- 
version of mechanical energy into electrical energy, by 
means of magneto-electric induction. 

MACHINE, D YNA MO-ELECTRIC, ALTERNATING-CUR- 
RENT — A dynamo-electric machine in which alternat- 
ing currents are produced. 

MACHINE, DYNAMO-ELECTRIC, BI-POLAR— A dynamo- 
electric machine, the armature of which rotates in a 
field formed by two magnet poles, as distinguished 
from a machine the armature of which rotates in a field 
formed by more than two magnet poles. 

Mi\ CHINE, DYNAMO-ELECTRIC, CLOSED-COIL— A dyna- 
mo-electric machine, the armature coils of which are 
grouped in sections, communicating with successive 
bars of a collector, so as to be connected continuously 
together in a closed circuit. 

MACHINE, DYNAMO-ELECTRIC, CLOSED-COIL DRUM— 
A closed-coil dynamo-electric machine, the armature 
core of which is drum-shaped. 



. 



MAC 398 

MACHINE DYNAMO-ELECTEIC, CLOSED-COIL RING— A 
elosed-coil dynaino-eleclric machine, the armature 
core of which is ring-shaped. 

MACHINE, DYNAMO-ELECTRIC, COMPOUND-WOUND— 

Machines whose field mai^nets are excited by more than 
one circuit of coils, or by more than a single electric 
sonrco. 

MACHINE, DYNA]NrO-ELECTRIC, CONTINUOUS-CUR- 
RENT — A dynamo-electric machine, the current of 
which is commuted so as to flow in one and the sam'3 
direction, as distinguished from an alternating dynamo. 

MACHINE, DYNAMO-ELECTRIC, EFFICIENCY OF— The 
ratio between the electric energj^ or the electrical 
horse-power produced by a dynamo, and the mechani- 
cal energy or horse-power expended in driving the 
dynamo. 

MACHINE, DYNAMO-ELECTRIC, FLASHING OF— A name 
given to long flashing sparks at the commutator, due to 
the short circuiting of the external circuit at the com- 
mutator, by arcing over the successive commutator in- 
sulating strips. 

IMACHINE, DYNAMO-ELECTRIC, MULTIPOLAR— A dyna- 
mo-electric machine, the armature of \vhieh revolves 
in a field formed by more than a single pair of poles. 

MACHINE, DYNAMO-ELECTRIC, OPEN-COIL— A dynamo- 
electric machine, the armature coils of which, though 
connected to the successive bars of the commutator, 
are not connected continuously in a closed circuit. 

MACHINE, DYNAMO-ELECTRIC, OPEN-COIL RING— An 
open-coil dynamo-electric machine, the armature core 
*»! which is ring-shaped. 



' 399 MAC 

MACHINE, DYNAMO-ELECTRIC, REVERSIBILITY OF— 
The ability of a dynamo to act as a motor when trav- 
ersed by an electric current. 

MziCHINE, DYNAMO-ELECTRIC, SEPARATELY EXCIT- 
ED — ^A dynamo-electric machine in wliich the field 
mag'net coils have no connection with the armature 
coils, but receive their currerit from a separate machine 
or source. 

MACHINE, DYNAMO-ELECTRIC, SERIES-AVOUND— A 
dynamo-electric machine, in wfiich the field circuit and 
the external circuit are connected in series with the 
armature circuit, so that the entire armatuire current 
must pr'Ss through the field coils. 

MACHINE, DYNAMO-ELECTRIC, SHUNT- WOUND— A 

dynamo-electric machine in which the field mag-net 
coils are placed in a shunt to the armature circuit, so 
that only a portion of the current generated passes 
through the field magnet coils, but all the difference of 
potential of the armature acts at the terminals of the 
field circuit. 
MACHINE, DYNAMO-ELECTRIC, SINGLE-MACxNET— A 
djmamo-electric machine, in which the field magnet 
poles are obtained by means of a single coil of insulated 
wire, instead of by more than a single coil. 

MACHINE. DYNAMO-ELECTRIC, SPARKING OF— An ir- 
regular and injurious operation of a dynamo-electric 
machine, attended \vitli sparks at the collecting 
brushes, 

MACHINE, DYNAMO-ELECTRIC, TO SHORT CIRCUIT A 
— To put a dynamo-electric machine on a circuit of 
comparatively small electric resistance. 



MAC 400 

MACHINF, ELECTROSTATIC INDUCTION— A machine in 
which a small initial charge produces a greatly increas- 
ed charge by its inductive action on a rapidly rotated 
disc of glass or other dielectric. 

Mx*. CHINE, ERICTIONAL ELECTRIC— A machine for the 
development of electricity by friction. 

MACHINE, HOLTZ— A particular form of electrostatic in- 
duction machine. 

MACHINE, INDUCTOR— An alternating current dynamo in 
vs^hich the field magnet projections are all of the same 
polarity. 

MACHINE, MAGNETO BLASTING— A magneto-electric 
machine employed for generating the current used in 
electric blasting. 

MACHINE, MAGNETO-ELECTRIC— A machine in \\'hich 
there are no field magnet coils, the magnetic field of 
the machine being due to the action of permanent steel 
magnets. 

MACHINE, RHEOSTATIC— A machine devised by Plante 
in which continuous static effects of considerable in- 
tensity are obtained by charging a number of condens- 
ers in multiple-arc and discharging them in series. 

MACHINE, TOPPLER-HOLTZ— A modified form of Holtz 
machine in which the initial charge of the armatures 
is obtained by the friction of metallic brushes against 
the armatures. 

MACHINE, WIMSHURST ELECTRICAL— A form of con- 
vection electric machine invented by Wimshurst. 



401 MAG 

MAGNET — A body possessing the power of attracting' the 
unlike pole of another magnet or of repelling the like 
pole; or of attracting readily magnetizable bodies like 
iron filings to either pole. A body possessing a mag- 
netic field. 

MAGNET, AKTIFICrAI.— A mag-net produced by induction 
from another magnet, or from an electric current. 

MAGNET, COMPOUND— A number of single magnets^ 
placed parallel and with thcif" similar poles facing one" 
another. 

MAGNET, DAMPING— Any magnet employed for the pur- 
pose of checking the velocity of motion of a moving 
body or magnet. 

MAGNET, ELECTEO— A magnet produced by the passage 
of an electric current through a (Toil of insulated wire 
surrounding a core of magnetizable material. 

MAGNET, ETECTl^O, HOHSESHOE- An electro-magnet, 
the core of which is in the shape of a horseshoe or U. 

MAGNET, ELECTKO, HUGHES'— An elecfro-magnet in 
which a U-sha]:)ed permanent magnet is provided with 
pole pieces of soft iron, on which only are placed the 
magnetizing coils. 

A quick-acting electro-magnet, in which the magnet- 
izing coils are placed on soft iron pole pieces that are 
connected with and form, the prolongations of flie poles 
of a permanent horseshoe magnet. 

MAGNET, ELECTRO, IRON-CLAD— An electro-magnet 
whose magnetizing coil is almost entirely surrounded 
by iron. 

MAGNET, HORSESHOE— A magneiized bar of steel or iron 
bent in the form of a horseshoe or letter U. 



MAG 402 

MAGNET, IROJS'-CLAD— A mag-net who^e mag-netic resist- 
ance is lowered by a casmg" of iron connected with the 
core and provided for the passage of the lines of mag-- 
netic force. 

MAGXET, KEEPER OF—A mass of soft iron applied to the 
poles of a magnet throngh which its lines of magnetic 
force pass. 

MAGXET, PEPtMAXENT— A magnet of hardened steel or 
other paramagnetic snbstance which retains its mag- 
netism for a long time after being magnetized. 

MAGXET, POPTATIVF POWER OF—The lifting power of 
a magnet. 

MAGXET, RELAY — ^An electro-magnet, whose coils axe 
connected to the main line of a telegraphic circuit, and 
the movements of whose armature is employed to bring 
a local battery into action at the receiving station, the 
current of which operates the register or sounder. 

MAGXET, FIELD, OF DYXA:M0-ELECTRIC :^L\CHIXE— 
One of the electro-magnets employed to produce the 
magnetic field of a dynamo-electric machine. 

MAGXETIC ATTRACTTOX- (See Attraction, Magnetic). 

MAGXETIC CIRCTTIJ— (See Circuit, Magnetic). 

MAGXETIC DEXSITY— (See Density, Magnetic). 

MAGXETIC FIELD— (See Field, Magnetic). 

MAGXETIC LEAKAGE— (See Leakage, Magnetic). 

MAGXETIC LIXES OF FORCE— (See Force, Magrnetic 
Lines of). 

MAGXETIC POLES— (See Poles, :\ragnetic). 



O' 



403 MAG 

MAGNETIC "RELUCTANCE— (See Reluctance, MaGrnetic). 
MAGNETIC UESTSTANCE— (See Eesistance, Magnetic). 
MAGNETIC STOEM— (See Storm, Magnetic). 

MAGNETIC WKT"RL- (See Whirls, Magnetic). 

MAGNETISM— That branch of science \^4iich treats of the 
nature and properties of magnets and the magnetic 
field. 

MAGNETISM, AMPERE'S THEORY OF— A theory or hypo- 
thesis proposed by Ampere, to account for the cause of 
magnetism, by the presence of electric currents in the 
ultimate particles of matter. 

MAGNETISM, ELECTRO— Magnetism produced by means 
of electric currents. 

MAGNETISM, EWING'S THEORY OF— A theory of mag- 
netism proposed by Prof. Ewing, based on the assump- 
tion of originally magnetized particles. 

MAGNETISM, HUGHES' THEORY OF— A theory pro- 
pounded by Hughes to account for the phenomena oi 
magnetism apart from the presence of electric currents. 

MAGNETISM, RESIDUAL— The magnetism remaining in 
the core of an electro-magnet on the opening of the 
magnetizing circuit . 

The small amount of magnetism retained by soft 
iron when removed from any magnetizing field. 

MAGNETISM, STRENGTH OF— A term sometimes used in 
the sense of intensity of magnetization. 

MAGNETIZABLE— Capable of being magnetized after the 
manner of a paramagnetic substance like iron. 



MAI 404 

MAGNETIZATION— The act of calling out or of eDdomiig 
with inagnetic properties. 

M:\GNETTZATION, INTENSITY OF— A quantity showing 
the intensity of the magnetization produced in a sub- 
stance. A quantity showing the intensity with which a 
magnetizable substance is magnetized. 

MAGNETIZATION, TME-LAG OF— A lag which appear*i 
to exist between the time of action of the macfnetizing 
force and the appearance of the magnetism. The time 
which must elapse in the case" of a given paramagnetic 
substance before a magnetizing force can produce mag- 
netization. ' , 

MAGNETIZE — To endow with magnetic properties. 

MAGNETO-ELECTEIC BELL— (See Bell, Magneto-Electric) 

MAGNETO-ELECTEIC BKAKE— (See Brake, Magneto- 
Electric). 

MAGNETOMETER— An apparatus for the measurement of 
magnetic force, 

MAGNETO-MOTIVE FOECE— (See Force, Magneto-Motive) 

MAIN, ELECTBIC— The principal conductor in any system 
of electric distribution. 

^EAIN, HOUSE — A term employed in a system of multiple 
incandescent lamp distribution for the conductor con- 
necting the house service conductors with a center of 
distribution, or with a street main. 

MAIN, STREET — In a system of incandescent lamp distri- 
bution the conductors extending in a system of net- 
works through the streets 'from junction box to junc- 
tion box, through which the current is distributed from 
the feeder ends, through cut-outs, to the district to be 
lighted, and from which service ^vires are taken. 



405 MET 

MAKE-AND-BREAK, AUTOMATIC— A term sometimes em- 
ployed for si]ch a combination of contact points with 
the armature of any electro-mag*net, that the circuit is 
automatically made and broken with great rapidity". 

MARrS"EK'S COMPASS— (See Compass. Azimuth). 

MATERIALS, INSULATING— Xon-conducting- substances 
which are placed around a conductor, in order that it 
may either retain an electric charge, or permit the pas- 
sage of an electric current through the conductor with- 
out sensible leakage. 

^MATTING, INAn:SIBLE ELECTBIC FLOOR— A matting or 
other -floor covering, provided with a series of electric 
contacts, which are closed by the passage of a person 
walking over them. 

:\rEDIUM, ELECT'EO-MAGNETIC— Any medium in which 
electro-magnetic phenomena occur, 

MEG OR MEGA (as a prefix)— 1,000,000 times; as, megohm, 
1,000,000 ohms; megavolt, 1,000,000 volts. 

MEGOHM— 1,000,000 ohms. 

METALLIC CIRCUIT— (See Circuit, Magnetic). 

METALLOID — A name formerly applied to a non-metallic 
body, or to a body having only some of the properties 
of a metal, as carbon, boron, oxygen, etc. 

METALLURGY, ELECTRO— That branch of applied science 
which relates to the electrical reduction or treatment 
of metals. Metallurgical processes effected by the 
agency of electricitj'. 

METER, A:\rPERE— (See Ampere-Meter. Ammeter). 



MIC 406 

METER, CUEREXT— A term now applied to an electric 
meter or galvanometer which measures the current in 
amperes, as '^isting'uished from one which measures 
the energ-y in watts. 

METER. ELECTRIC— Any apparatus for measuring com- 
mercially the quantity of electricity that passes in a 
given time through any consumption circuit. 

METER, ELECTRO-CHEMICAL— An electric meter in 
which the current passing is measured by the electro- 
lytic decomposition it etJects. 

METER, ELECTRO-MA€XETIC— An electric meter In 
which the current passing is measured by the electro- 
magnetic effects it produces. 

METER, E>TERGY~A term sometim.es applied to a watt 
meter. 

METER, MTLLT- AMPERE— An ampere meter graduated to 
read milli-amperes. 

METER, WATT — An instrument generally consisting of a 
galvanometer constructed so as to measure directly the 
product of the (rarrent, and the diiference of potential. 

MHO — A term proposed by Sir Wm. Thomson for the prac- 
tical unit of cond^lctivit^ . Such a unit of conductivity 
as is equal to the reciprocal of 1 ohm. 

MICA — A maneral substance employed as an insulator, 

MICA, MOL'LDED — An insulating substance consisting of 
finelj^ divided mica made into a paste, with some fused 
insulating substance, and moulded into any desired 
shape. 



407 MOR 

MICRO (os a prefx) — The one-millionth; as, a microfarad^ 
the millionth of a farad; a microvolt, the one-millionth 
of a volt. 

MICEO-FAEA.I)— (See Farad, Micro). 

MTCEOPHONE— An apparatus invented by Prof. Hnghei? 
for rendering- faint or distant sounds distinctly audible, 

MIL — A unit of length eqiial to the 1-1000 of an inch, or .001 
inch, used in measuring- the diameter of wires. 

MIL, CIECLTLAR — A unit of area emijloj-ed in measuring^ 
the areas of cross-sections in wires, equal to ,78540 
square mil. The area of a circle one mil in diameter. 

MIL, SQUARE — A unit of area employed in measuring- the 
areas of cross-sections of wires, equal to .000001 square- 
inch. One square mil equals 1.2732 circular mil. 

MILLI (as a prefix) — The one-thousandth part. 

MILLI-AMPERE — The thousandth of an ampere. 

]^^^^E, ELECTRO-CONTACT— a submarine mine that is 
fired automatically on the completion of the current 
of a battery placed on the shore through the closing of 
floating contact points by passing vessels. 

MIRROR GALVANOMETER— (See Galvanometer, Mirror). 

MORSE ALPHABET— (See Alphabet, Telegraphic: Morse's) 

MORSE RECORDER— (See Recorder, Morse). 

MORSE SYSTEM OF TELEGRAPHY— (See Telegraphy, 
Morse System of). 

MORSE'S TELEGRAPHIC ALPHABET— (See Alphabet^ 
Telegraphic: Morse's). 



MOT 408 

MOTIOX, SIMPLE-HAI^MOXIC— Motion which repeats it- 
self at reg-ular intervals, taking- place backwards or 
for^vards, and ^vhich may be studied by comparison 
with nniform motion round a circle of reference. 

MOTOGRAPH, ELECTRO— A land speaking telephone in- 
vented hj Edison whereby -the friction of -a platinum 
point against a rotating cylinder of moist chalk, is re- 
duced b3" the passage of an electric current. 

JMOTOR, COMPOUXD-WOUND— An electric motor whose 
field magnets are excited by a series and a shunt wire. 

:M0T0R, ELECTRIC— a device for transforming electric 
jjower into mechanical power. 

MOTOR, ELi:CTRIC, ALTERXATIXG-CURREXT— An elec- 
tric motor driven or operated by means of alternating 
currents. 

MOTOR, ELECTRIC, DIRECT-CURREXT— An electric m.o- 
tor driven or operated by means of direct or continuous 
electric currents, as distinguished from a motor driven 
or operated bj' alternating currents. 

MOTOR, ELECTRIC, SLOW-SPEED— An electric motor so 
constructed as to run with fair efficiency at slow speed. 

MOTOR, PYROIVIAGXETIC— A motor driven by the attrac- 
tion of magnet poles on a movable core of iron or nickel 
unequally heated, 

MOTOR, ROTATES G-CURREXT— An electric motor design- 
ed for use with a rotating electric current. 

MOTOR, SERIES-WOUXD— An electric motor in which the 
field and armature are connected in series with the 
external circuit as in a series dynamo. 



, 



409 NEB 

MOTOE, SHUXT-WOUXD— An electric motor in which the 
field magnet coils are placed in a shunt to the armature 
circuit. 

MULTIPHASE CURKENT— (See Current, Multiphase). 
IMUITIPHASE DYyA]\TO~(See Dynamo, Multiphase). 
MULTIPHASE SYSTE]M— rSee System, Multiphase). 
MULTIPLE-SEEIES— A multiple connection of series 
groups. 

N 

N. — A contraction employed in mathematical writings for 
the whole number of lines of magnetic force in any 
magnetic circuit. 

N. — A contraction for Xorth Pole. 

KEEDLE, .^STATIC— A compound magnetic needle of great 
sensibility, possessing little or no directive power. 

An astatic needle consisting of two separate magnet- 
ic needles, rigidly connected together and placed par- 
allel and directly over each other, with opposite poles 
opposed. 

NEEDLE, MA.GNETIC— A straight bar-shaped needle of 
magnetized steel, poised near or above its center of 
gravit}^ and free to move either in a horizontal plane 
only, or in a vertical plane only, or in both. 

NEEDLE, MAGNETIC, DAMPED— A magnetic needle so 
placed as to quickly conie to rest after it has been set 
in motion. 

NEEDLE, MAG^'ETIC, DECLINATION OF— The angular 
deviation of the magnetic needle from the true 'geo- 
graphical north. The variation of the magnetic needle. 

21 



NIC xiO 

NEEBLE, ^sIAGXE'nC, DEFLECTIOX OF-The moTement 
of a needle out of a position of rest in the earth's mag- 
nelie field or in the field of another mag-net, bj' the 
action of an electric current or another Jiag'net. 

XEEDT.E, ^^FACyETIC, DIPPIXG— A raagneic needle sus- 
pended so as to be free to inove in a vertical plane, em- 
ployed to determine the angle of dip or the magnetic 
inclination. 

NEEDLE, Mx^GXETIC, DIRECTIVE TEXDEXCY OF— The 

tendency of a magDctic needle to mo^e so as to come 
to rest in the direction of the lines of the earth's mag- 
netic Held. 

NEEDLE, TELEGEAPinC— A needle employed in telegra- 
phy to represent by its movements to the left or right 
respectively the dots and dashes of the MorSe alphabet. 

XEGATIVE ELECTPODE— (See Electrode, Xegative). 

XEGATIVE ELE:SIFXT OF A VOLTAIC CELL— (See Ele- 
ment, Xegative, of a Voltaic Cell). 

X^EGATIVE FEEDEPS— (See Feeders, Xegative). 

XEGATIVE POLE— (See Pole. Xegative). 

XEUTRA]. FEEDER— The feeder that is connected with 
the nentral or intermediate terminal of the dynamos 
in a three-wire system of distribution. 

NEETRAL LINE OF CO:\nrrTATOP C^T.IXTDER— (See 
Line, Xentra], of Commntator Cylinder). 

XELTTRAL POTXT— (See Point, Xentral). 

NEUTRAL POIXTS OF DYX'A:NrO-ELECTRIC :NrACHIX&- 

(See Points, Xentral, of Dynamo-Electric Machine). 
NICKJ5L-PLATIXG-(See Plating, Xicl>-el). 



411 OIL 

NOX-COXDUCTOES — Substances that olTer so o-reat resist- 
ance to the passage of an electric current through their 
mass as to practically exclude a discharge passing 
throuefh them. 



OHM — The unit of electrical resistance. 

Such a resistance as would limit the flow of electric- 
it^' under an electromotive force of one volt to a cur*^ 
rent of one ampere, or to one coulomb per second. 

OIIAr, B. A.- -A contraction for British Association ohm. 

OHM, BOAED OF TRADE— A unit of resistance as deter- 
mined by a committee of the English Board of Trade. 

Oinr, BP.ITISn ASSOCTATIOX— The British Association 
unit of resistance, adopted prior to 1884. 

OH^Nf, LEG AT.,— The resistance of a column of mercury 1 
square millimetre in area of cross-section, and 106 centi- 
metres in length, at the temperature of degree C. or 
22 degrees F, 

OHM, MEG— One million ohms. 

OHMTC RESISTAXCE— (See Resistance, Ohmic or True). 

OHMIMETER — A commercial galvanometer, devised by x\yr- 
ton. for directly measuring by the deflection of a mag- 
netic needle, the resistance of any part of a circuit 
through which a strong current of electricity isflo^Wng. 

OHM'S LAW— (^ee Law of Ohm). 

OILJLXSULATOR— (See Insulator, Oil). 

OIL TRANSFORMER— (See Transformer, Oil). 



PAR 412 

OPE^^-CIRCUIT VOLTAIC CELT.-(See Cell, Voltaic, Open- 
Circuit). 

OPEN-CIRCUITED— Put on an open circuit. ^ 

OPEX-COIL DRT::\r dynamo-electric :\L\CITINE— (See 
Machine, Dynamo-Electric, Open-Coil Drum). 

OSCILLATIONS, ELECTRIC— The series of partial, inter- 
mittent di«^char5res of which the apparent instantane- 
ous discharge of a Leyden jar through a small resist- 
ance actually consists. 

OSMOSE, ELECTRIC— A differeuce of liquid level between 
two liquids on opposite sides of a diaphragm produced 
by the passage of a strong electric current through the 
liquid? between two electrodes placed therein. 



P. D. OR p. d. — A contraction frequently employed for dif- 
ference of potential. 

PACINOTTI RING- (See Ring, Pacinotti). 

PAIR, ASTATIC — A term sometimes applied to an astatic 
couple. 

PAPAEFINE — A name given to various solid hydrocarbons 
of the marsh gas series, that are derived from coal or 
petroleum by the action of nitric acid. 

PARAMAGNETIC — Possessing properties ordinarily recog- 
nized as magnetic. Possessing the power of concen- 
trating the lines of magnetic force. 

PARAMAGNETIS^NT — The magnetism of a paramagnetic 
substance. 



413 PHA 

PETTIEK EFFECl — (See Effect, Peltier). 

PENDANT, ELECTRIC— A hangino- fixture provided with a 
sooV.et for the support of an incandescent lamp. 

PENDANT, FLEXIBLE ELECTPvIC LKiHT— V pendant for 
an incandescent lamp formed by the flexi15!e conductors 
which support the lamp. 

PENDULUM, ELECTKIC— A pendulum so arranged that its 
tto-ajid-fro moftdon send electric impulses over a line, 
either by makinof or breaking contacts. 

PFT^IODIC CUIiPENT, POWER OF— The rate of transform^ 
ation of the energy of a circuit traversed hy a simple 
periodic current. 

PERIODICITY- The rate of chamge in the alterations or 
pulsations of an electric current. 

PERMANENT MAGNET VOLTMETER-^ (See Voltmeter, 
Permanent Magnet). 

PERMEABILITY CURVE— (See Curve, PermeabiUty). 

PERMEABILITY, MAGNETIC— Conductibility for lines of 
magnetic force. 

The ratio existing between the magnetization pro- 
duced, and the magnetizing force producing such ma^*- 
netization. 

PERMEAMETER— An apparatus devised by S. P. Thomp- 
son for roughly measuring the magnetic permeability. 

PHASE, ANGLE OF DIFFFRENCE OF, BETWEEN AL- 
TERNATING CURRENTS OF SAME PERIOD- The 
angle which measures the shifting of phase of a simple 
periodic current with respect to another due to lag or 
other cause. 



PHO 414 

PHASE, SHIFTING OF, OF ALTERXATING CURRENT— 

A chansre ir. pJiase of current due to magnetic lag or 

other causes. 
PHONE — A term frequently used for telephone. 
PHONOGRAM — A record produced by the phonograph. 

PHONOGRAPH — An apparatus for the reproduction of ar- 
ticulate speech, or of sounds of any character, at any 
indefinite time after their occurrence, and for any 
nnnjber of times. 

PHOSPHORESCENCE, ELECTRIC — Phosphorescence 
caused In a substance b}" the passage of an electric dis- 
charge. 

PHOSPHORESCENCE, PHYSICAL— Phosphorescence pro- 
duced in matter hy the actual impact of light wave? 
resulting in a vibratory motion of the molecules of suf- 
ficient rapidity to cause them to emit light. 

PHOSPHORUS— El^ECTRIC S:MELTING OF— An electric 
process for the direct pror'uction of phosphorus. 

PHOTO^IETER — An apparatus for measuring the Intensity 
of the light emitted by any luminous source. 

PHOTOMETER. ACTINIC— A photometer in which the in- 
tensity of any light is measured b^^ the amount of 
chemical decomposition it ellects. 

PHOTOMETER, DISPERSION— A photometer in w^hieh the 
light to^be measured is decreased in intensity a known 
amount so as to more readily permit it to be compared 
with a standard light of much smaller intensity. 

PHOTO^METER, SHADOW— A photometer in which the in- 
tensity of the light to be measured is estimated by a 
comparison of the distances ai which it cr.^i a standard 
light produce a shadow of ihe same intensity. 



115 PIT 

PHOTOMETER, T"RANSLUCENT DISC— A photometer in 
which the light to be measured is placet! on one side of 
a partly translncent and partly opaqne disc, and a 
standard candle is placed on the opposite side, and the 
mtensit}' of the light estLmated by the distaiices of the 
light from the disc when an equal illumination of all 
parts of the disc is obtained. 

PHOTOPHONE— An instrument invented by Bell for the 
telephonic transmission of articulate speech along a 
ray of light instead of along a conducting wire. 

PIECES, POLE, OF DYNAMO-ELECTEIC MACHINE— 
Masses of iron connected with the poles of the Held 
magnet frames of dynamo-electric machines, and shap- 
ed to conform to the outline or contour of the armature. 

PILE, DRY — A voltaic pile or battery consisting of nu- 
merous cells, the voltaic coupl'e in each of w^hich con- 
sists of sheets of paper covered wdth zinc-foil on one 
disc and black oxide of manganese on the other. 

PILE, TIIEEMO, DIEFEPvEXTIAL— A thermopile in 
which the tw^o opposite faces are exposed to the 
action of two nearly equal sources of heat in order to 
deternnne accurately the differences in thermal in- 
iensities of such sources of heat. 

PILE, TriEHMO-ELECTPIC— A number of separate ther- 
mo-electric couples, united in series, so as to form a 
single thermo-electric source. 

PILOT LAMP— (See Lamp, Pilot.) 

PIN, INSULATOR— A bolt by means of which an insulator 

is attached to the telegraphic support or arm. 
PITH BALL- (See Balls, Pith.) 



^LA 416 

PLANE, PROOF — A sraall insulated conductor employed 
to take test charg-es from the surfaces of insulated, 
charged conductors. 

PLAT — ^A word sometimes used for installation, or for the 
npparntus required to carry on any manufacturing 
operation. 

PLANTS, ELECTETCITY OF— Electricity produced natur- 
ally by plants during their vigorous growth. 

PLATTE, NEGATIYF, OF STORAGE CELL— Tliat place of 
a storage cell which, by the action of the charging 
current, is converted iuto or partly covered with a 
coating of spongy lead. 

PLATE, NEGATIVE, OF VOLTAIC CELL— The electro- 
negative eleruent of a voltaic couple. 
That element of a voltaic couple \\'hich is negative in 
the electrolyte of the cell. 

PLATE, POSITIVE, 01' STORAGE BATTERY— That plate 
of a storage battery which is converted into, or 
covered by, a layer of lead peroxide, by the action of 
the charging current. 

That plate of storage battery which is connected 
with the positive terminal of the charging source and 
which is, therefore, the positive pole of the battery 
on discharging. 

PLATE, I'^OSITIVE. OF VOLTAIC CELL— The electro- 
positive in the electrolyte of the cell. 

PLATES OF SECONDARY^ OR STORAGE CELL, FORM- 
ING OF — Obtaining a thick coating of lead peroxide 
on the lead plates of a storage battery, by repeatedly 
sending the charging current through the cell alter- 
nately in opposite directions. 



417 PLU 

PLATING, ELECTED— The process of coveriug- any elec- 
trically conducting- surface with a metal by the aid 
of the electric current. 

PLATING, NICKEL— Electro-plating- with nickel. 

PLATING, SILYEE— Electro-plating- A^ath silver. 

PLOW — The sliding- contacts connected to the motor of 
an electric street car, and placed within the slotted 
underground conduit, and provided for the purpose 
of taking- ofP the current from the electric mains 
placed therein, as the contacts are pushed forward 
over them by the motion of the ('ar. 

PLUG— A piece of metal in the shape of a plug-, provided 
for making- or breaking- a circuit by placing* in, or re- 
moving- from, a conical opening- formed in the ends 
of two closely approached pieces of metal which are 
connected with the circuits to be made or broken. 

PLUG, SAFETY— A wire, bar, plate or stripe of readily fus- 
ible metal, capable of conducting-, without fusing, the 
current ordinarily employed on the circuit, but which 
fuses, and thus breaks the circuit, on the passage of 
an abnormal current. 

PLUG, SHORT-CTECUITING— A plug by means of which 
one part of a circuit is cut out by being" short-cir- 
cuited. 

PLL^G, WALL — A plug pro\'ided for the insertion of a 
lamj) or other electro-receptive device in a wall soc- 
ket, and thus connecting it with a lead. 

PLUCKS, GEIB— Plugs of active material that fill the spaces 
or apertures in the lead grid or plate of a storage bat- 
tery. 



POL -^^^ 



PLUNGE BATTEEY— (See Battery, Plunge.) 

POINT, CAKBON— A term formerly applied to the car- 
bon electrodes used in the production of the voltajc 



arc. 



POTNTTS, NEUTEAI. OE DYNAINIO-T-'LECTEIC MACHINE 
—Two points of greatest difierence of potential, sit- 
L^ated on tLe commntator c^iinder, at the opposite 
ends of a diameter thereof, at which the collecting- 
brushes m.nst rest in order to carry off the current 
quietly. 

POLAPvlTY, :MAGNETIC— The polarity acquired by a 
mag-netizable • substance when brought into a mag- 
netic fjeld. 

POLARIZATION— A counter E. :NL F. produced by the pas- 
sage of a current, through an electric couple or battery. 

POIAEIZED AB:MATURE— See Armature, Polarized. 

POLE CHANGER— A switcli or ]<ey for changing or re- 
versing the direction of current produced by any elec- 
tric source, such as a battery, 

POLE, CONSEQUENT— A magnet pole formed by two free 
north or two free south poles placed together. 

POLE, :SL\GNETIC, EREE— A poil© in a piece of iron, or 
other paramagnetic substance, which acts as if it ex- 
isted as one m^agnetic pole only. 

POLE, MAGNETIC, NORTH— That pole of a magnetic 
needle which points approximately to the earth's geo- 
gfraphical north. 



419 POL 

POLE, :\L\GXETTC, XOP.TII-SEEKTXG— That pole of a 
' magnetic needle whieli jioiiits apj)roxini:itely towards 
the earth's geographical north. 

POLE, MAGNETIC SALIENT— A term sometimes applied 
to the single poles at the extremities of an anomalous 
magnet in order to distinguish them from the double or 
conseqnent pole formed by the juxaposition of two 
similar magnetic poles. 

POLE, MAGNETIC, SOUTH— That pole of a magnetic 
needle which points approximately towards the earth's 
geographical south. 

The ^- on th -seeking pole of a magnetic needle. 

POLE, NEGATI^Tv-That pole of an electric sonrce 
through which the current is assumed to enter or flow 
bade into the source after having passed through the 
circuit external to the source. 

POLE, POs;iTlYE— That pole of an electric source out of 
which the electric current is assumed to f!ow. 

POLi:, TELEGEAPHIC— A w^ooden or iron upright on 
which telegraphic or other wires are hung. 

POLE, TROLLEA^— The pole which supports the trolley 
bearing and rests on tlie socket in the trolley base 
frame in an overhead wire electric railway system. 

POLES, ]\L\GNETIC— The tw^o points where the Hues of 
magnetic force pass from the iron into the air, and 
from tjie air into the iron. 

The tW'O points in a magnet where the magnetic 
force appears to be concentrated. 



POT 420 

POPGUN, ELECTEO-MAGXETIC— A magnetizing- coil, 
provided with a tubular space for the insertion of a 
core, much shorter than the length of the coil, which, 
when the energizing current is passed through the 
coil, is thrown violent h" out from the coil. 

POKOUS CUP— (See Cup, Porous.) 

POSITIVE DIRECTION OF LINES OE MAGNETIC FORCE 
— (See Force, ^Magnetic, Lines of, Positive Direction 
of.) 

POSITIVE PLATE OF STORAGE BATTERY— See Plate, 
Positive, of Storage Battery.) 

POSITm^. PLATE OF VOLTAIC CELL— (See Plate, Posi- 
tive, of Voltaic Cell.) 

POSITIVE POLE— (See Pole, Positive). 

POST, BINDING — A device for connecting the terminal 
of an electric source with the terminal of an electro- 
receptive device, or for connecting different parts of 
an electric apparatus with one another. 

POTENTIAL, ALTERNATING— A potential, the sign of 
direction of which is alternately changing from posi- 
tive to negative. 

POTENTIAL CONSTANT— A potential which remains con- 
stant under all conditions. 

POTENTIAL, DIFFERENCE OF— A term employed to de- 
note that portion of the electromotive force which 
exists between any two points in a circuit. 

POTENTIAL, ELECTRIC— The power of doing electric 
work. 
Electrical leveL 



421 POW 

POTENTIAL, FALJj OP— A decrease of potential in the 
direction in which an electric current is flowing-, pro> 
portion al to the resistance when the current is con- 
stant. 

POTENTIAL, MAGNETIC— The amount of work required 
to bring- uj) a unit north -seeking magnetic pole from 
an inlinite distance to a given point ii^. a magnetic 
field. 

POTENTIAL, UxN^IT DIEFERENCE OF— Such a difference 
of potential between two points that requires the ex- 
penditure of one erg of work to bring a unit of posi- 
tive electricity^ from one of these points to another, 
against the electric force. (See Erg.) 

The practical unit of difference of potential is the 
volt. 

POTENTIOMETER— An apparatus for the galvanometer 
measurement of electromotive forces, or differences of 
potential, by a zero method. 

POWER— Eate of doing work. 

Mechanical power is generally measured in horse 
power, which is equal to w^ork done at the rate of 550 
foot-pounds per second. 

POWER, CANDLE— An intensity of light emitted from a 
luminous body equal to the light produced by a stand- 
ard candle. 

POWER, CANDLE, NOAIINAL— A term sometimes applied 
to the candle-power taken in a certain favorable direc- 
tion. 

This term is generally used in arc lighting. In the 
ordinary arc lamp the greatest amount of. light is 
emitted at a particular point, viz: from the crater ii? 
the upper or positive carbon. 



PRI 4225 

POWER, CANDLE, SPHERICAL— The average or mean 
value of candle pov^^er taken at a number of points 
around the source of lig-ht. 

POWER, CONDUCTING, FOR ELECTRICITY -The ability 
of a given length and area of cross-section of a sub- 
stance to conduct electricity, as compared with an 
equal length and area of cross-section of some other 
substance, such as pure silver or copper. 

POWER, ELECTRIC— Power developed by means of elec- 
tricity. 

POWER, ELECTRIC, DISTRIBUTION OF— The distribu- 
tion of electric power by means of any suitable system 
of generators, connecting circuits and electric motors. 

POWER, ELECTRIC TRANSMISSION OF— The transmis^ 
sion of mechanical energy by converting it into elec- 
tric energy at one point or end of a line, and recon- 
verting at some distant point from electrical to me- 
chanical energy. 

POWER, HORSE— A rate of doing work equal to 550 foot- 
pounds per second, or 33,000 foot-pounds per minute. 

POWER, HORSE, ELECTRIC— Such a rate of doing electric 
work as is equal to 746 watts per second. 

This rate is equivalent to 33,000 foot-pounds per min- 
ute, or 550 foot-pounds per second. 

POWER, PROJECTING, OF MAGNET— The power a mag- 
net possesses of throwing or projecting its lines of 
magnetic force across an intervening air space or gap. 

PRESSURE WIREvS— (See Wires, Pressure). 
PRIMARY COIL— (See Coil, Primary). 



^ 



423 QUA 

PRIMARY, THE— That conductor in an induction coil, or 
transformer, v.hich receives the impressed electromo- 
tive force, or which carries the inducing- current. 

PRIME CONDUCTOR— (See Conductor Prime). 

PROXY BRAKE— (See Brake, Prony). 

PLT^L, ELECTRIC BELT— A cir^.uit-closing- de\ice operated 
by a pull. 

PULSATUSTG CURRENT— (See Current, Pulsating). 

PUMP, AIR, MERCURIAL— A device for obtaining a high 
vacuum by the use of mercury. 

PUMP, AIR, SPRENGEL^S MERCURIAL— A mercurial air 
pump in which the vacuum is obtained by means of the 
fall of a stream of mercury. 

PUSH — A name sometimes applied to a push button, or to 
a floor push. 

PUSH BUTTON— (See Button, Push). 

PYRO-ELECTRICITY— (See Electricity, Pyro). 

PYROMETER, SIEMEN'S ELECTRIC— An apparatus for 
the determination of temperature by the measurement 
of the electric resistance of a platinum wire exposed 
to the heat whose temperature is to be measured. 



QUADRATURE, IN— A term employed to express the fact 
that one simple periodic quantity lags 90 degrees be- 
hind another. 

QUANTITY, UNIT OF ELECTRIC— A definite amount or 
quantity of electricity called the coulomb. 



BAI 424 



R, — A contraction used for ohmic resistance. 

RADIATION, ELECTEO-MAGNETIC— The sending ot:-; in 
all directions from a conductor, through which an os- 
cillating discharge is passing, of electro-magnetic waves 
in all respects similar to those of light except that they 
are of mnch greater length, 

EAILKOAD, ELECTRIC— A railroad, or railway, the cars 
on which are driven or propelled by means of electric 
motors connected with the cars. 

RAILROADS, AUTOMATIC ELECTRIC SAFETY SYSTEM 
FOR — A system for automatically preventing the ap- 
proach of two trains at any speed beyond a predeter- 
ing safety from collisions of moving railroad trains by 
dividing the road into a number of blocks or sections 
of a given length, and so maintaining telegraphic com- 
munication between towers located at the ends of each 
of such blocks as to prevent, by the display of suitable 
signals, more than one train or engine from being on 
the same block at the same time, 

IcAILROADS, ELECTRIC, CONTINUOUS OVERHEAD 
SYSTEM OF MOTIVE POWER FOR— A variety of the 
dependent system of motive power for electric railroads 
in which a continuous bare conductor is connected with 
the terminals of a generating dynamo, and supported 
overhead by suitable means, and a traveling wheel or 
trolley is moved over the same by the motion of the 
car, in order to carry ofE the current from the line to 
the car motor. 



425 RAl 

RAILrvOADS, ELECTKIC, CONTINUOUS SURFACE SYS- 
TEM OF MOTIVE POWEK FOR— A variety of the de- 
pendent system of mqtive power for electric railroads, 
in whicli the terminals of the generating- dynamo are 
connected to the continuous bare metallic conductor 
that extends along- the entire track on the s^irface of 
the roadway or street, and from which the current is 
taken off by means of a traveling* conductor connected 
with the moving- car. 

RAILROADS, ELECTRIC, CONTINUOUS UNDERGROUND 
SYSTEM OF MOnVE POWER FOR— A variety of the 
dependent system of motive power for electric raih 
ways, in which a continuous bare conductor is placed 
underg-round in an open slotted conduit, and the cur- 
rent taken off from the same by means of sliding or 
roiling contacts carried on the moving car. 

RAILROADS, ELECTRIC, DOUBLE-TROLLEY SYSTEM 
FOR — A. system of electric railroad propulsion, in which 
a double trolley is employed to take the driving cur- 
rent from two overhead trolley wires. 

RAILROADS, ELECTRIC, INDEPENDENT SYSTEM OF 
MOTIVE POWER FOR— A term for the electric pro- 
pulsion of railway cars by means of primary or storage 
batteries placed on the car and directly connected with 
the motor, 

KAILROADS, ELECTRIC, SINGLE-TROLLEY SYSTEM— 
A system of electric railroad propulsion in which a 
single trolley is employed to take the driving current 
from a single overhead trolley wire. 

28 



EEC 426 

KAY, ELECTRIC— A species of fish named the ray, which, 
like the electric eel, possesses the power of producing 
electricity. 

EECETYEE, liATaiOXIC— A receiver, employed in systems 
of harmonic teleg-raphy, consisting of an electro-mag- 
netic reed; tnned to \ibrate to one note or rate only. 

EECEIVEK, PTIONOGEAPHIC— The apparatus employed 
m a telephone, phonograph, graphophone or gramo- 
phone for the reproduction of articulate speech. 

EECEIVER, TELEPHOXIC— The receiver employed in the 
telephone. 

EECOED, GEAMOPHONE— The irregular indentations, cut- 
lings or tracings marie by a point attached to the dia- 
Xohragm spoken against, and employed in connection 
with the receiving diaphragm for the reproduction of 
articulate speech. 

EECOEDEE, CHEMICAL, BAIX'S— An apparatus for re- 
cording the dots and dashes of a ^lorse telegraphic dis- 
patch, on a sheet of chemically prepared paper. 

EECOEDEE, MOESE— An apparatus for automatically re-, 
cording the dots and dashes of a Morse telegraphic dis- 
patch, on a fillet of paper drawn under an indenting 
or marking* point on a striking lever, connected ^\ath 
the armature of an electro-magnet. 

EECOEDEE, SIPHOX— An apparatus for recording in ink 
on a sheet of paper, by means of a fine glass siphon 
supported on a fine wire, the message received over a 
cable. 

EECTIFIED — Turned in one and ^* same direction. 



427 EEL 

EEFLECTTNG GALVANOMETER— (See Ualvanometer, Re- 
!lectinf»") , 

REGISTER, TELEGRAPPITC— An apparatus employed at 
the receiving- end of a telegraphic line for the purpose 
of obtaining- a permanent record of the telegraphic 
dispatch. 

REGISTER, WATCHMAN'S ELECTRIC— A device for per- 
manently recording the time of a watchman's visit to 
each of the different localities he is required to visit at 
stated intervals. 

REGULATION, AUTOMATIC, OF DYNAMO-ELECTRJC 
[MACHINE — Such a regulation of a dynamo -electric 
machine as will automaticall\ present constant either 
the current or the potential difference. 

REGULATION, HAND- Such a regulation of a dynamo- 
electric machine as ^vill preserve constant, either the 
current or the potential, said regulation being etfected 
by hand as distinguished from automatic regulation. 

REGULATOR, AUTOMATIC— A device for securing auto- 
matic regulation as distinguished fromhand regulation. 

KELAY — An electro-magnet, employed in systems of tel- 
egrapliy, provided with contact points placed on a deli- 
cately supported armature, the movements of which 
throw a battery, called the local battery, into or out 
of the circuit of the receiving apparatus. 

RELAY, DIFFERENTIAL— A telegraphic relay containing 
two differentially wound coils of wire on its magnet 
cores. 

RELAY MAGNET — A name sometimes given to a relay. 



KES 428 

RELAY, MICEOPHONE— A devnee for autoinatically repeat- 
ing- a telephonic message over another wire. 

RELAY, POLAKTZED-A teleoTaphle relay provided ^vith a 
permanently magnetized armature in piace of the soft 
iron armature of the ordinary instrument. 

RELUCTANCE, MAGNETIC—A term recently proposed in 
place of magnetic resistance to ex:press the resistance 
offered by a medium to the passage through its mass 
of lines of magnetic force. 

RELUCTANCE, MAGNETIC, UNIT OF- -Such a magnetic 
reluctance in a closed circuit that i)ermits unit mag- 
netic flux to traverse it under the action of unit mag- 
neto-motive force. 

REPEATERS, TELEGRAPHIC-Telegraphic devices v.here- 
hy the relay, sounder or regiotering apparatus, on the 
opening and closing of another circuit, ^^itli which it is 
.suitably connected, is caused to repeat the signals re- 
ceived. 

REPULSION, ELECTRO-DYNAMIC— The mutual repulsion 
between two electric circuits whose currents are flow- 
ing in opposite directions. 

REPULSION, ELECTRO-MAGNETIC-The mutual repul- 
sion produced by two similar electro-magnetic poles. 

REPULSION, ELECTROSTATIC— The mutual repulsion 
produced by two similar electric cliarges. 

REPULSION, MAGNT:TIC— The mutufil repulsion exerted 
between two similar magnetic poles. 

RESIDUAL MAGNETISM— (See Magnetism, Residual). 



^29 REa 

EESIN — A g'eneial terni applied to a variety of dried juices 
of vegetable orififin. 

RESISTANCE — Something- placed in a oircr.it for the pur- 
jjose of opposing* the passag-e or fiow of the current in 
the circuit or branches of the circuit in which it is 
placed. 

The electrical resistance of a conductor is that quality 
of the conductor in virtue of which there is a fixed nu- 
merical ratio between the potential difference of the 
two opposing- faces of a cubic unit of such conductor, 
and the quality of electricity which traverses either 
face per second, assuming- a steady flow to take place 
normal to these faces, and to be uniformly distributed 
over them, such flow taking* place solely by an electro- 
motive force outside the volume considered. 

RESISTANCE, ABSOLUTE UNIT OF— The one thousand 
millionth of an ohm. 

RESISTANCE POX— (See Box, Resistance). 

RESISTANCE COIL— (See Coik Resistance). 

RESISTANCE, EFFECT OF HEAT ON ELECTRIC— Nearly 

all uietallie conductors have their electric resistance 
increased by an increase of temperature. 

The carbon conductor of an incandescent electric 
lamp, on the contrary, has its resistance decreased 
when raised to electric incandecsence. The decrease 
amounts to about three-eig-hths of its resistance when 
cold. 

RESISTANCE, ELECTRIC— The ratio between the electro- 
motive force of a circuit and the current that passes 
therein. The reciprocal of electrical conductivity. 



RES 430 

EESISTAXCE, ELECTKIC, OF LIQUIDS— The resistance 
oft'eied by a liquic} mass to the passage of an electric 
ciirrent. 

As a rule the electric resistances of liquids, with the 
single exception of mercury, are enormously higher 
than tlxose of metallic bodies. 

r.ESISTAXCE, FALSE— A resistance arising from a coun- 
ter electromotive force and not directly from the di- 
mensions of the circuit, or from its specific resistance. 

RESISTANCE, IXDUCTIVE— A resistance which possesses 
self-induction. 

RESISTANCE, IXSULATIOX— The resistance of a line or 
conductor existing between the line or conductor and 
tlie earth through the insulators, or between the two 
wires of a cable through the insulating material sepa- 
rating them. 

RESISTANCE, MAGNETIC— The reciprocal of magnetic 
permeability or conductibility for lines of magnetic 
. force. Resistance offered by a medium to the passage 
of the lines of magnetic force through it. 

RESISTANCE, NON-INDItCTIYE— A resistance in which 
self-induction is practically absent. 

RESISTANCE, OPIMIC^-The true resistance of a conductor 
due to its dimensions and specific conducting power, as 
distinguished from the spurious resistance produced 
by a counter electromotive force. 

RESISTANCE, OR CELL, SELENIUM-^A mass of crystal- 
line selenium, the resistance of ^vhich is reduced by 
placing it in the form of narrow strips between the 
edges of broad conducting plates of brass. 



b 



431 RHE 

RESIST AN^CE, SECONDARY-^A lerm sometimes used in 
place of external secondary resistance. 

RESISTxVA^CE, SPECIFIC— ^nie particular resistance wliich 
a substance offers to the passag-e of electricity throuf^rh 
it. 

RESISTANCE, UNIT OF— Snch a resistance tEat unit dif- 
ference of potential is required to cause a current of 
unit strength to pass. (See Ohm). 

RESOXAXCE, ELECTRIC— The setting up of electric pulses 
in open-circinted conductors, hj the action of pulses in 
neighboring conductors. 

RESONATOR, ELECTRIC— An apparatus employed by 
Hertz in his investigations on electric resonance. 

RESULTAXT--In mechanics, a single force that represents 
in direction and intensity the ei?ects of tv^o or more 
separate forces. 

RETARDATION- A decrease in the speed of telegraphic 
signaling' caused either by the induction of the line 
conductor on itself, or by mutual induction between it 
and neighboring conductors, or by condenser action, 
or by all. 

REVERSIP>ILITY OF DYNAMO— The ability of a dynamo 
to operate as a motor when traversed by an electric 
current. 

REVERSING IvEY—fSee I\ey, Reversing). 

RHEOSTAT— An adjustable resistance. 

A rheostat enables the current to be brought to a 
standard, i. e., to a fixed value, b3^ adjusting the resist- 
ance; hence the name. 



RUK 432 

RHEOSTAT, WATEK— A rheostat the resistance of which 
is obtained by means of a mass of water of fixed di- 
mensions. 

KING PACINXOTTI— A kind of grame ring- containing- 
spaces or grooves for wire bobbins formed in the iron 
of the ring. 

ROCKEE, BRUSH — Tn a djnamo-electric machine or elec- 
tric motor, any device for shifting- the position of the 
brushes on the commutator cylinder. 

ROD, CLUTCH — A clutch or clamp provided in an arc lamp 
to seize the lamp ro'd and thus arrest its fall, during 
feeding, beyond a certain point. 

ROD, LAMP — A metallic rod provided in electric arc lamps 
for holding the carbon electrodes. 

ROD, LIGHTIS'IXG— A rod, or wire cable of good conduct- 
ing material, placed on the outside of a house or other 
structure, in order to protect it from the effects of a 
lightning discharge. 

ROD, LTGHTXTXG, POINTS ON— Points of inoxidizable 
material, placed on lightning rods, to effect the quiet 
discharcre of a cloud by convection streams. 

ROSETTE — An ornamental plate provided with contacts 
connected to the terminals of the service wires, and 
placed in a wall for the ready attachment of the in- 
candescent lamp. 

A word sometimes used in place of rose. 

ROTARY-PHASE CURRENT— (See Current, Rotating). 

ROTATING CURRENT— (See Current, Rotating). 

RUHMKORFF COIL— (See CoiL Rhumkorff). 



■iHo SEO 

s 

S. — A contraction employed for second. 

SATE RATION, ]\rAGNETIC— The maximum mag-netization 
which can be imparted to a mag-hetic substance. 

The condition of iron, or other paramagnetic sub- 
stance, when its intensity of mag'netization is so great 
that it fails to be further sensibly magnetized by any 
magnetic force, however great. 

SCALE, THEElMO:\rETER, CEXTTGRADE— A thermometer 
scale, in which the length of the thermometric tube 
between the melting point of ice and the boiling point 
of water is divided into one hundred equal parts or 
degrees. 

SCALE, THE"R]^rOME7•ER, FAHEEXHEIT'S— A thermom- 
eter scale in which the length of the thermometer tube 
between the melting point of ice and the boiling point 
of water is divided into 180 equal parts called degrees. 

SCREEX, :>.rAGNETIC— A hollow box whose sides are made 
of thick iron, placed around a magnet or other body 
so as to cut it ofl- or screen it from any magnetic field 
external to the box. 

SCREENING, MAGNETIC— Preventing magnetic induction 
from taking place by interposing a metallic plate, or a 
closed circuit of insulated wire, between the body pro- 
ducing the magnetic field and the body to be mag- 
netically screened. 

SECOND, WATT— A unit of electrical work. 

SECONDARY BATTERY— (See Battery, Secondary). 



^Kit 434 

SECONDARY COIL— (See Coil, Secondary). 

SECOXDARY, MOVABLE— The secondary conductor of an 
induction coil, which, irstead of being- fixed as in most 
coils, is movable. 

SECTION, TROLLEY- A sing-le continuous length of trol- 
ley wire, with or without its branches. 

SEISMOGRAPH, MICRO— An electric apparatus for photo- 
graphically resfistering* the vibrations of the earth pro- 
duced by earthquakes or other causes. 

SELENIUM — A comparatively rare element generally found 
associated with sulphur. 

SELENIUM CELL— (See Cell, Selenium). 

SELE-INDUCTION— (See Induction, Self). 

SEMAPHORE — A variety of signal apparatus employed in 
railroad block systems. 

SEPARATOR — An insulating sheet of ebonite, or other 
similar substance, corrugated and perforated so as to 
conform to the outline of the plates of a storage bat- 
tery, and placed between them' at suitable intervals, in 
such a manner as to avoid short-circuiting, without 
impeding the free circulation of the liquid. 

SERIES, CONTACT— A series of metals arranged in such 
an order that each becomes positively electrified by 
\ contact with the one that follows it. 

SERIES DISTRIBUTION OF ELECTRICITY BY CON- 
STANT CURRENTS— (See Electricity, Series Distribu- 
tion of, by Constant Current Circuit), 



435 SHU 

SEETES, THERMO-ELECTRIC— A list of metals so arrang- 
ed according to their thermo-electric powers, that each 
metal in the series is electro-positive to any metal 
lower in the list. 

SERIES TURNS OF DYNAMO-ELECTRIC MACHINE— (See 
Turns, Series, of Dynamo-Electric Machine). 

SERIES WINDING— (See Winding, Series). 

SERIES-WOUND DYNAMO- (See Dynamo, Series). 

SHELLAC — A resinous substance possessing valuable insu- 
lating properties, which is exuded from the roots and 
branches of certain tropical plants. 

SHOCK, ELECTRIC— The physiological shock produced in 
an animal bv an electric discharo-e. 

SHORT-CIRCUIT— To establish a short circuit. 

SHUNT — An additional path established for the passage 
of an electric current or discharge. 

SHUNT — To establish an additional path for the passage 
of an electric current or discharge. 

SHUNT CIRCUIT— (See Circuit, Shunt). 

SHUNT DYNAMO-ELECTRIC MACHINE— (See Machine, 
Dynamo-Electric, Shunt-Wound) . 

5^HUNT, GALVAN01\[ETER— A shunt placed aroimd a sen- 
sitive galvanometer for the purpose of protecting it 
from the effects of a strong current, or for altering its 
sensisbility. 

SHUNT, MAGNETIC— An additional path of magnetic ma- 
terial provided in a magnetic circuit for the passage of 
the lines of force. 



SPA 436 

SHUTTLE AKMATTJRE— (See Armature, Shuttle.) 

SILVER TLATTNG— (See Plating, Silver.) 

SIPHON, ELECTRIC-— A siphon in which the stoppage of 
flow, due to the gradual accunanlation of air, is pre- 
vented by electrical means. 

SMELTESG, ELECTRO— The separation or reduction of 
metallic substances from their ores by means of electric 
currents. 

SXAP SWITCH— (See Switch, Snap.) 

SOCKET, ELECTRIC LAMP— A support for the reception 
of an incandescent electric lamp. 

SOCKET, WALL — A socket placed in a w^all and provided 
with, openings for the insertion of a wall plug with 
w^hich the ends of a flexible twin-lead are connected. 

SOLENOID — A cyclindrical coil of wire the convolutions of 
which are circular. 

An electro-magnetic helix. 

SOLENOID CORE— The core, usually of soft Iron, placed 
within a solenoid and magnetized by the magnetic field 
of the current passing through the solenoid. 

SOLUTION, BATTERY— The exciting liquid for voltaic 
cells. (See Cell, Voltaic.) 

SOURCE, ELECTRIC — Any arrangement capable of main- 
taining a difl'erence of potential or an electromotive 
force. 

SPARK COIL— (See Coil, Spark.) 
SPARK, GAI»— (See Gap, Spark.) 



437 STA 

SPARKI^G, LTXE OF LEAST— The line on a commutator 
cylinder of a dynamo connecting the points of contact 
of the collecting briishea where the sparking is a mini- 
mum. 

SPAEKIXG OF DYXA:M0-ELECTKIC MACHIXE— (See Ma^ 
chine, Dynamo-Electric, Sparking of.) 

SPECIFIC IXDITCTIVE CAPACITY— (See Capacity, Speci- 
fic. 
SPHEEICAL AE:NrATUKE— (See Armature, Spherical.) 
SPIDEE, AEMATITKE- A light framework or sketetou 
consisting of a central sleeve or hub keyed to the arma- 
ture shaft, and provided with a number of radial 
spokes or arms for fixing or holding the armature core 
to the d,yna mo-electric machine. 

SPKIXG-JxACK-— A device for readily inserting a loop in a 
main electric circuit. The spring-jack is generally 
used in connection with a multiple switch board. 

STAGGEEIXG — A term sometimes applied to the position 
of the brushes on a commutator cylinder, in which one 
brush is placed slightly in advance of the other brush 
so as to bridge over a break. 

STAXDAED, BYX A:\rO— The supports for the bearings of 
a dynamo-electric machine. 

STATIOX, CEXTEAL— A station, centrally located, from 
which electricity for light or power is distributed by a 
series of conductors radiating therefroni. 

STATIOX, TEAXSFOEMIXG— In a system of distribution 
by transformers or converters a station where a number 
of transformers are placed, in order to supply a group 
of houses in the neighborhood. 



SUS 438 

STOOL, INSULATING— A support isolated from the ground 
usually by glass insulators. 

STORAGE BATTLKY— (See Battery, Storage.) 

STORAGE CELL— (See Cell, Storage.) 

STOEM, ELECTKIC— An unusual condition of the atmos- 
phere as regards the quantity of its free electricity. 

STOEM, M;\GNETTC— Irregularities occurring in the dis- 
tribution of the earth's magnetisin, affecting the mag- 
netic declination, dip, and intensity. 

STEEXGTH, FIELD— The intensity or total flux of magn- 
etism of a dynamo. 

STRIPPING — Dissolving the metal coating from a silver- 
plated or other metal-plated article. 

SUBMARINE CABLE— (See Cable, Submarine.) 

SUBWAY, ELECTPJC — An accessible underground way or 
passage provided for the reception of electric wires or 
cables. 

Sl'LPHATING- -A nam.e applied to one of the sources of 
loss in the operation of a storage battery, by means 
of the formation oi: a coating of inert sulphate of lead 
on the battery plates. 

SL^SCEPTIBILITY, MAGNETIC— The ratio existing be- 
tsveen the induced magnetization and the magnetic 
force producing such magnetism, or the intensity oi 
magnetism divided by the magnetic force. 

SUSPEX'SION, BI FILAR— The suspension of a needle by 
iwo parallel wires or fibres, as distinguished from a 
suspension by a single wire or fibre. 



439 SWI 

SlTSPEXSTOiS", KXIFE-EDGE— The suspension of a needle 
on knife edges that are supported on steel or agate 
planes. 

SWITCH BOAKD- (See Board, Switch.) 

SWITCH, BREAIC-DOWX— A special switch, employed in 
small three-wire systems, for connecting the positive 
and negative bus-wires in such a manner as to prac- 
tically convert it into a two-wire system and permit 
the system to he supplied with current from a single 
dynamo. 

SWITCH, CHAXGTXG— A switch designed to throw a cir- 
cuit from one electric source to another. 

SWITCH, J)OUBI,]^-BREAK KXIFE— A knife switch pro- 
vided with double-break contacts. 

Sn^TTCH, DOUBLI'-POLE— a switch that makes or breaks 
contact with both poles of the circuit in which it is 
placed. 

A switch consisting of a combination of two separate 
switches, one connected to the positive lead and the 
other to the negative lead. 

SWITCH, FEEDFri— The switch employed for connecting 
or disconnecting each conductor of a feeder from the 
bus-bars in a central station. 

SVflTCH, KXIFE- -A switch^ which is opened or closed by 
the motion of a knife contact which moves between 
parallel contact plates. 
A knife-edge switch. 

SWITCH, BfiYETJSTNG— A switch for reversing the direc- 
tion of a circuit. 



TAG 440 

SWITCH, SNAP— A switch in which the transfer of the 
contact points from one position to another is acccm- 
plished b}^ means of a quick motion obtained by the 
operation of a spring*. [^ 

SWITCH, TELEPHONE, AUTOMATIC— A device for auto^ 
matically transferring the connection of the main Jine 
from the call bell to the telephone circuit. 

SWITCH, THEEi:-POINT— A switch by means of which 
a circuit can be completed through three different con- 
tact points. 

SWITCH, TIME— An automatic switch in which a prede- 
termined time is required either to insert a resistance 
in or remove it from a circuit. 

SWITCH, TWO-POINl'— A switch by means of which 
a circuit can be completed through two different 
contact points. 

SYSTE:\r, THREE-WIRE— A system of electric distribution 
for lanjps or ether translating devices connected' in 
multiple, in which three wires are used instead of the 
two usually employed. 

In the three-w^ire system tw^o dynamos are generally 
employed, which are connected with one another in 
series. 

T 

T. — A symbol used for time. 

TACHOMETER — An apparatus for indicating at any mo- 
ment on a revolving dial the exact number of revolii- 
tions per minute of a shaft or machine. 






441 TEL 

TALK, CEOSS — In telephony an indistinctness in the 
* speech transmitted over any circuit, due to this circuit 
receiving", either by accidental contacts or by induction, 
the speech transmitted over neighboring circuits. 

TANNING, ElrECTRIC— An application of electric currents 
to tanning leather. 

I^APE, INSULATING— A ribbon of flexible material im- 
pregnated with kerite, okonite, rubber or other suitable 
insulating material, employed for insulating wires or 
electri3 conductors at joints, or other exposed places. 

T \STE, GALVANIC — A sensation of taste produced when 
a voltaic current is passed through the tongue or in the 
neighborhood of the gustatory nerves, or nerves of 
c-aste. 

TEASER, ELECTRIC CURRENT— A coil of fine wire placed 
on the field magnets of a dynamo-electric machine, 
next to the series coil wound thereon, and connected 
as a shunt across the main circuit. 

This term is also used to designate the auxiliary 
winding us^ed for producing the polyphase current in 
a monocyclic dynamo. 

TECHNICS, ELECTRO— The science whicli treats of the 
physicol applications of electricity and the general 
princii)les applying thereto. 

TELEGRAPHIC— Pertaining to telegraphy. 
TELEGRAPHIC ALPHABET— (See Alphabet, Telegraphic.) 
TELEGRAPHIC CABLE— (See Table, Telegraphic.) 

TELEGRAPHIC CODE— (See Code. Telegraphic.) 

29 



TEL 442 

TELEGEAPHIC KEY— (See Key, Teleg-raphic.) 

TELEGEAPHING — Sending- a communication by means of 
telegraphy. 

TELEGEAPHY, ACOUSTIC— A non-recording system of 
telegraphic communication,* in which the dots and 
dashes of the Morse system, or the deflections of the 
needle in the needle systems, are replaced by sounds 
that follow one another at intervals, that represent 
the dots and dashes, or the deflections of the needle, 
and thereby the letters of the alphabet. 

TELEGEAPHY AND TELEPHOXY, SIMULTANEOUS, 
OVEE A SINGLE WIEE— Any system for simultaneous 
transmission of telegraphic and telephonic messages 
over a single wire. 

TELEGEaPELY, AUTOMATIC— a system by means of 
which a telegraphic message is automatically trans- 
mitted by the motion of a previously perforated fillet 
of paper containing perforations of the shape and order 
required to form the message to be transmitted. 

TELEGEAPHY, CHEMICAL— A system by means of which 
the closings of the mainline-circuit, corresponding to 
the dots and dashes of the Morse alphabet, are recorded 
on a lillet of paper by the electrolytic action of the cur- 
rent on a chemical substance with which the paper 
fillet is impregnated. 

TELEGEAPHY, DIPLEX— A method of simultaneously 
sending- two messages in the same direction over a sin- 
gle wire. 

Diplex telegraphy is to be distinguished from duplex 
telegraphy, where two messages are simultaneously 
transmitted over a single wire in opposite directions, 



443 TEL 

TELEGKAPHY, DLrPLEX, BRIDGE METHOD OF— A sys- 
tem whereby two telegraphic messages can be simul- 

• taneoiisly transmitted over a sing-ie wire in opposite 
directions. 

'J ELEGFvAPHY, DUPLEX, DTFFEPEXTIAL METHOD OF 
— A system of duplex telegraphy in which the coils of 
the receiving" and transmitting- instruments are differ- 
entially wound. 

TELEGRAPHY, FAC-SIMILE— A system whereby a fac- 
simile or copy of a chart, diagram, picture or signature 
is telegraphically transmitted from one station to 
another. 

TELI:GRAPHY, fire ALARTT— a system of telegraphy 
by means of which alarms can be sent to a central sta- 
tion, or to the fire engine houses in the district, from 
call boxes placed on the line. 

TELEGRAPHY, GRAY'S H7^Ri>I0NIC MLTLTIPLE-A sys- 
tem for the simultaneous transmission of a number* of 
separate and distinct m.usical notes over a single wire, 
which separate tones are utilized for the simultaneous 
transnsissibn of an equal number of telegraphic mes- 
sages. 

TELEGRAPHY, LSDUCTION— A system of telegraphing 
by induction between moving trains and fixed stations 
on a railroad, bj^ means of impulses transmitted by in- 
duction between the car and a wire parallel with the 
track. 

l^ELEGRAPHY, INDUCTION, CURRENT SYSTEM OF— A 
system of induction telegraphy depending on current 
induction between a fixed circuit along the road, cind a 
parallel circuit on the moving train. 



TEL 444 

Q'ELEGRAPHY, INDUCTIO]^*, STATIC SYSTElNf OP— A 
system of inductive telegraphy depending- on the static 
induction between the sending- and receiving* instru- 
ment. 

TELEGRAPHY, MORSE SYSTEM OF— A system of tele- 
graphy in which makes and breaks occurring* at inter- 
vals corresponding* to the dots and da:^hes of the Morse 
alphabet are received by an electro-magnetic sounder 
or receiver. 

TELEGRAPHY, MLT:.TIPLEX— A system of teleg*raphy for 
the simultaneous transmission of more than four sepa- 
rate messages over a sing*le wire. 

TELEGRAPHY, PRINTING— A system of telegi-aphy ip 
which the messag*es received are printed on a paper iih 
let. 

TELEGRAPHY, QUADRUPLEX— A system for the simul- 
taneous transmission of four messag-es over a single 
wire, two in one direction and the remaining two in 
the opposite direction. 

TELEGRAPHY, QUADRUPLEX, BRIDGE ]\rETHOD OF— 
A system of quadruplex telegraphy by means of a 
double bridge duplex system. 

TELEGRAPHY, QUADRUPLEX, DIFFERENTIAL ]NrETH- 
OD OF — A system of quadruplex telegraphy by means 
of a double dilTerential duplex system. 

TELEGRAPHY. SIMPLEX— A system of telegraphy in 
which in a single message only can be sent over the 
line. 



445 THE 

TELEGRAFHY, STEP-BY-STEP— A system of telegraphy 
in which the signals are registered by the movements 
of a needle over a dial on which the letters of the al- 
phabet, etc., are marked. 

TELEGRAPHY, SUBMAEINE— A system of telegraphy in 
which the line wire consists of a submarine cable. 

TELEGRAPHY, SYNCHRONOUS-MULTIPLEX, DELANY'S 
SYSTEM!— A system devised bj^ Delany for the simul- 
taneous telegraphic transmission of a number of mes- 
sages either all in the same direction, or part in one 
direclion and the remainder in the opposite direction. 

TELEGRAPHY, WRITING— A species of fac-simile tele- 
graphy ^ by means of which the motions of a pen at- 
tached to a transmitting instrument so vary the resis- 
.% tance on two lines connected with a receiving instru- 
ment as to cause the current received thereby to re- 
produce the motions, on a pen or stylus, which trans- 
fers them to a sheet of paper. 

A sytem of writing telegraphy consists essentially of 
transmitting and receiving instrujnents connected by a 
double line wire. 

TELEPHONE — An apparatus for the electric transmission 
of articulate speech. 

TELEPHONIC EXCHANGE— (See Exchange, Telephonic, 

System of). 
TER3riNALS — A name sometimes ay>plied to the poles of a 

battery or other electric source, or to the ends of the 

conductors or wires connected thereto. 
THERAPEUTICS, ELECTRO, OR ELECTRO-THERAPY— 

The application of electricity to the curing' of disease. 



TOU 446 

THEPvMO-ELECTKIC BATTERY— (See Battery, Thermo- 
Electric.) 

THEKMO-ELECTRTC COUPLE- (See Couple, Thermo-Elee- 
tric.) 

TIJERMO!\rETEE, ELECTRIC RESISTANCE— A thermo- 
meter the action of which is based on the change in 
the electric resistance of metallic substances with 
changes in temperature. 

TKEROMSTAT — An instrument for automatically miaintain- 
ing" a given temperature by the closing of an electric 
circuit through the expansion of a solid or liquid. 

THERMOSTAT, MERCURIAL- -A thermostat operating by 
the expansion of a mercury column. 

TITREE-WTRE SYSTEM— (See System, Three-Wire.) 

TICKER SERVICE, STOCK- -The simultaneous transmis- 
sion of stock quotations or other desired information 
to a number of subscribers. 

TIPS, POLAR — The free ends of the field magnet pole 
pieces of a dynamo-electric machine. 

TORQUE — That moment of the force applied to a dynamo 
or other machine which turns it or causes its rotation. 
The mechanical rotary or turning force which acts 
on the armature of a dynamo-electric machine or mo- 
tor and causes it to rotate. 

TOUCH, DOUBLE—A method of magnetization in which 
two closely approximated magnet poles are simultane- 
ously dra^vn from one end of the bar to be magnetized 
to the other and back again, and this repeated a num- 
ber of times. 



447 TRA 

, TRACTION, MAGNETIC— The force w^ih which a magnet 
holds on to or retains its armature, when once attached 
thereto. 
TRAMWAY, EL7^:CTRIC— A railway over which cars are 
driven by means of electricity. 
An electric railroad. 
TRANSFORMER— An inverted Ruhmkorff induction coil 
employed in systems of distribution by means of al- 
ternating* currents. 

An apparatus for raising or lowering the voltage of 
an electric current used in /transmitting and distribut- 
ing power. 

A transformer is sometimes called a converter. The 
word transformer is, however, the one most employed. 
^/TRANSFORMER, CLOSED IRON CIRCUIT— A transformer 
the core of which forms a complete magnetic circuit. 

These transformers are sometimes called ironclad 
transformers. 
TRANSFORMER, CONSTANT-CURRENT— A transformer 
in which a current of a constant potential in the pri- 
mary js converted into a current of constant strength 
in the secondary, despite changes in the load on the 
secondary. 
TRANSFORMER, CORE— A transformer in which the pri- 
mary and secondary wires are wrapped around the out- 
side of a core consisting of a bundle of soft iron wires 
or plates. 
TRANSFORMER, EFFICIENCY OF— The ratio between the 
whole energy supplied in any given time to the pri- 
mary circuit of a transformer and that which appears 
in the form of electric current in the secondary circuit. 
TRANSFORMER, HEDGEHOG— A name applied to a par- 
ticular form of open-iron circuit transformer. 



TEA 448 

TKANSFOHMER, MULTIPLE— Any form of transformer 
which is connected in multiple to the primary circuit. 

TRANSFORMEK, OIL- -A transformer which is immersed 
in oil in order to insure a high insulation. 

TEAIN^SFORMER, EOTARY-CURRENT— A transformer 
operated by means of a rotary current. 

TANSFORMER, SHELIr— A transformer in which the pri- 
mary and secondary coils are laid on each other, and 
the iron core is then wound through and over them so 
as to enclose all the copper of the primary and sec- 
ond ai*y circuits within the iron. 

TRANSFORMER, STEP-DOWN— A transformer in which a 
small current of comparatively great difference of po- 
tential is converted into a large current of comparative- 
ly small difference of potential. 

TRANSFORMER, WELDING— A transformer suitable for 
changing a small electric current of comparatively high 
difference of potential, into the heavy currents of low 
difference of potential required for welding purposes. 
Welding transformers have in general a very low re- 
sistance in their secondary coils, and almost invariably 
consist of a single turn or at the. most of a few turns 
of very stout wire. 

TRANSLATING DEVICE— (See Device, Translating.) 

TRANSMITTER, CARBON, FOR TELEPHONES— A tele- 
phone transmitter consisting of a button of compressi- 
ble carbon. 

The sound waves impart to-and-fro movements to the 
transmitting diaphragm, and this to the carbon but- 
ton, thus varying its resistance by pressure. This but/- 
ton is placed in circuit with the battery and induction 
coil. 



449 TUB 

TItANSMITTEK, ELECTRIC— A name applied to various 
electric apparatus employed in telegraphy or telephony 
to transmit or send the electric impulses over a line 
wire or conductor. 

TREATMENT, HYDRO-CARBON, OF CARBONS— Exposing 
carbons, while electrically heated to incandescence, to 
the action of a carbonizing gas, vapor or liquid, for the 
purpose of rendering them more uniformly electrically 
conducting throughout. 

TRIMMING — A term sometimes applied to the act of plac- 
ing the carbons in an electric arc lamp. 

TROLLEY — A rolling contact wheel that moves over the 
overhead lines proxided for a line of electric railway 
cars, and carries off the current required to drive the 
motor car. 

TROLLEY, DOUBLE— The traveling conductors, which 
move more over the lines of wire in any system of 
electric railways that employs two overhead conduc- 
tors. 

TROLLEY POLE— (See Pole, Trolley). 

TUBE, CROOKES'— A tube containing a high vacuum and 
adapted for showing any of the phenomena of the 
ultra-gaseous state of matter. 

TUBES, YACUUAf-Glass tubes, from which the air has 
been partially exhausted and through which electric 
discharges are passed for the production of luminous 
effects. 

TURN, AMPERE — A single turn or vdnding in a coil of 
wire through which one ampere passes. 



CJNI 450 

TURNS, 3EKIES, OF DYNAMO-ELECTKTC MACHINES-- 
The ampere-turns in the series circuit of a compound- 
wound dynamo-electric machine. 

TURNS, SHUNT, OE DYNAINIO-ELECTRIC MACHINE— 
The ampere-turns in the shunt circuit of a couij>r.und- 
wound dynamo-electric machii^e. 

u 

UNITS, ABSOLUl^E— A system of units basi-d on the centi- 
metre for the unit of length, the gramme for the unit 
of mass, and the second for the unit of time. 

UNITS, CENTIMETRE-GRAMME-SECOND— A system oi 
units in which the centimetre is adopted for the unit 
of length, the gramme for the unit of mass, and the 
second for unit of time. 

UNITS, C. G. S. — The centimetre-gramme-seeond units. 

UxVITS, FUNDAMENTAL— The units of length, time and 
mass, to which all other quantities can be referred. 

UNITS, HEAT— Units based on the quantity of heat re- 
quired to raise a given weight or quantity' of a sub- 
stance, generally water, one degree. 

The principal heat units are ihe English heat unit, 
the greater and smaller calorie and the joule. (See 
Calorie. Joule.) 
UNITS, MAGNETIC— Units based on the force exerted be- 
tween two magnet poles. 

Unit strength of a magnetic pole is such a magnetic 
strength of pole that repels another magnetic pole of 
^ equal strength placed at unit distance with unit force, 
or witJi the force of one dyne. 



451 VIB 

UNITS. PKACTTCAL— Multiples or I'rnctions of the abso- 
lute or centiinetregramme-seeouci units. 



V — A contraction sometimes used for volt. 

V — A contraction sometimes used for velocity. 

VACUUM, HIGH — A space from which nearly all traces 
of air or residual gas have been removed. 

Such a vacuum that the length of the mean free path 
of the molecules of the residual atmosphere is equal to 
or exceeds the dimensions of the containing* vessel. 

VACUUM, TORKICELXIAN— The vacuum VN^hich exists 
above the surface of the mercury in a barometer tube 
or other vessel over thirty inches in vertical height. 

VARIATION, MAGNETIC— Variations in the value of the 
magnetic declination, or inclination, that occur simul- 
taneously^ over all the parts of the earth. 

VARNISH, ELECTRIC^An insulating material dissolved in 

a solvent. 
When the varnish is dry it should produce a layer or 

film of insulating material. 
VIBRATION OR WAVE, AlMPLITUDii] OP— The ratio that 

exists in a wave between the degree of condensation 

and rarefaction of the medium in which the wave is 

propagated. 

VIBRATION, PERIOD OF— The time occupied in execut- 
ing one complete vibration or motion to-and-fro. 

VIBRATIONS, ISOCmiONOUS— Vibrations which perform 
their to-and-fro motions on either side of the position 
of rest in equal times. 



VOL 452 

VIBKATIONS, SYMPATHETIC— Vibrations set up in 
bodies by waves of exactly the same wave rate as these 
produced by the vibrating body. 

VIS-VIVA— The energy stored in a moving* body, and there- 
fore the measure of the amount of work that must be 
performed in order to bring* a moving body to rest. 

VOLT — The practical unit of electro-motive force. 

Such an electromotive force as would cause a current 
ductor which ciits lines of magnetic force at the rate 
of 100,000,000 per sec. 

Such a electromotive^ force as would cause a current 
of one ampere to flow against tlie resistance of one 
ohm, . 

VOLT-AMMETER— A wattmeter. 

A variety of galvanom.eter capable of directly meas- 
uring the product of the difference of potential and the 
amperes. 

VOLT AMPERE— A watt. 

VOLTAGE — This term is now very commonly used for 
either the electromotive force or difference of potential 
of any part of a circuit as determined by the reading 
of a voltmeter placed in that part of the circuit. 

VOLTAIC ARC— (See Arc, Voltaic.) 
VOLTAIC BATTERY— (See Battery, Voltaic.) 
VOLTAIC CELL— (See Cell, Voltaic.) 
VOLTAIC ELEMENT— (See Element, Voltaic.) 
VOLTAMETER— An electrolytic cell employed for meas- 
uring the quantity of the electric current passing 
through it by the amount of chemical decomposition 
effected in a given time. 



453 VOL 

VOLTAMETER, COPPER— A voltameter Tn which the 
quantity of the current passin^^ is determined by the 
weig-ht of copper deposited. 

VOLTAMETER, VOLUME--A voltameter In which the 
quantity of the current passing- is determined by the 
volume of the g-ases evolved. 

VOLTMETER — An instrument used for measuring- differ- 
ence of potential. 

VOLTMETER, CARDEW'S— A form of voltmeter in which 
the potential difference is measured by the amount of 
expansion caused by the heat of a current passing 
through a fixed resistance. 

VOLTMETER, CLOSED-CIRCUIT— A voltmeter in which 
the points of the circuit, between which the potential 
difference is to be measured, are connected with a 
closed coil or circuit, and which gives indications by 
means of the current so produced in said circuit. 

VOLTMETER, GRAVITY— A form of voltmeter in which 
the potential difference is measured by the movement 
of a magnetic needle against the pull of a weight. 

VOLTMETER, MAGNETIC- VANE— A vol+meter in which 
the potential difference is measured by the repulsion 
exerted between a fixed and a moveable vane of soft 
iron placed within the field of the magnetizing coil. 

VOLTMETER, MULTI-CELLULAR ELECTROSTATIC— An 
electrostatic voltmeter in which a series of fixed and 
movable plates are used instead of the single pair em- 
ployed in the quadrant electrometer. 



WAT *±o4 

VOLTMETER, OPEN-CIRCUIT—A voltmeter in which the 
points of the circuit where potential difference is to be 
measured are connected with an open circuit and give 
indications by means of the charges so produced. 

VOLTMETER, PERMANENT MAGNET— A form of volt- 
meter in which the difference of potential is measured 
by the movement of a magnetic needle under the com- 
bined action of a coil and a permanent magnet, against 
the ptill of a spring. 

VULCABESTON — An insulating substance composed of as- 
bestos and rubber. 

VULCANITE — A variety of vulcanized rubber extensively 
used in the construction of electric apparatus. 

Vulcanite is sometimes called ebonite from its black 
color. It is also sometimes called hard rubber. 

w 

W — A contraction sometimes used for watt. 

WALL SOCKET— (See Socket, Wall.) 

WATCHES, DEMAGNETIZATION OF— Processes for re- 
moving magnetism from watches. 

WATT — The unit of electric power. The volt-ampere. 

The power developed when 44.25 foot-pounds of work 
are done per minute, or 0.7375 foot-pounds per second. 
The 1-746 of a horse power. 

WATT-HOUR- A unit of electric work. 

A term employed to indicate the expenditure of an 
electrical power of one watt, for an hour. 



455 WKB 

WATT-HOUR, KILO— The Board of Trade unit of v/ork 
equal to an output of one kilo-watt for one hour. 

WATT, KILO— One thousand watts. 

A unit of power sometimes used in stating- the out- 
put of a dynamo. 

WATT-METEK — A galvanometer by means of which the 
simultaneous measurement of the difference of poten- 
tial and the current passing* is rendered possible. 

The w^att-meter consists of tw^o coils of insulated 
wire, one coarse and the other jBue, placed at right 
angles to each other as in the ohm-meter, only, Instead 
of the currents acting on a suspended magnetic needle, 
they act on each other as in the electro-dynamometer. 

WAVE — A disturbance in an elastic medium that is periodic 
both in space and time. 

WAVE, ELECTRIC— An electric disturbance in an elastic 
medium that is periodic T)oth in space and time. 

WAVES, ELECTRO-MAGNETIC— AVaves in «ie ether that 
are given off from a. circuit through which an oscillat- 
ing discharge is passing, or from a magnetic circuit 
undergoing variations in magnetic intensity. 

WELDING, ELECTRIC— Effecting the welding union of 
metals by means of heat of electric origin. 

In the process of Elihu Thompson, the metals are 
heated to electric incandescence by currents obtained 
from transformers, and are subsequentify pressed ot 
Ijammered together. 

WHEEL, TROLLEY— A metallic w^heel connected with the 
trolley pole and moved over ^ the trolley wire on the 
motion of the car over the tracks, for the purpose of 
taking the curicent from the trolley wire by means of 
rolling contact therewitJx, 



WIE 456 

WHIHL, ELECTRIC— A term employed to indicate the cir- 
cular direction of the lines of magnetic force snrronnd- 
ing a conductor convejdng an elastic current. 

WHIRL, MAGNETIC— The lines of magnetic force which 
surround the circuit of the conductor conreying an 
electric current. 

WIXDIXG, A^IPERE— A single winding or turn through 
which one ampere passes. 

Ampere-winding is used in the same signification as 
ampere-turn. 

WTLXDIXG, COMPOUXD, OF ]:)YXAMO-ELECTRIC MA- 
CHIXE — A method of winding in which shunt and ser- 
ies coils are placed on the field magnets. 

WIXDIXG, SERIES — A winding of a dynamo-electric ma- 
chine in which a single set of magnetizing coils are 
placed on the field magnets, and connected in series 
with the armature and the external circuit. 

WIRE, DEAD. OF ARMATURE— That part of the wire on 
the armature of a dynamo which produces no electro- 
motive force or resultant current. 

WIRE, DEPLEX — An insulated conductor containing two 
separate parallel wires. 

WIRE. FEEDIXG— A term sometimes applied to the wire 
or lead of a multiple circuit which feeds the main. 

In a system of electric railroads the feeding wires 
feed the trolley wires. 

WIRE, FL'SE — A readily fusible w^re employed in a safety 
catch to open the circuit when the current is excessive. 



457 WIB 

WIRE, HOUSE— In a system of incandescent electric light- 
ing any conductor that is connected with a service con- 
ductor and leads to the meter in the honse. 

WIRE, INSUIiATED— Wire covered with any insulating ma-' 
terial. 

WIRE, IJNE— In telegraphy the wire that connects the 
different stations with one another. 

WIRE, NEGATIVE— A term sometimes applied to that wire 
of a parallel circuit which is connected to the negative 
pole of a source. 

WIRE, NEUTRAL— The middle wire of a three-wire system 
of electric distribution. 

WIRE, POSITIVE— The wire or conductor connected to the 
positive pole or terminal of any electric source. 

WIRE. SLIDE — A wire of uniform diameter employed in 
Wheatstone's electric bridge for the proportionate arms 
of the bridge. 

WIRE, SPAN — The wire employed in systems of electric 
railways for holding the trolley wire in place. 

WIRE, TROLLEY— The wire over which the trolley passes 
in a system of electric railways, and from which the 
current is taken to drive the motors on the cars. 

WIRES, DEAD — Disused and abandoned electric wires. 
WIRES, LEAI)ING-IN— The wires or conductors which lead 
the current through (into and out of) an electric lamj). 

WIRES, PILOT— In a system of incandescent lighting, 
where a comparatively low potential is employed on 
the mains, thin w^ires leading directly from the gener- 
ating station to different parts of the mains, in order 

to determine the differ^nQ^s of potential at such points. 

30 ^ 



YOK 458 

WIRES, PRESSURE— Tn a system of incandescent electric 
lig-htiDg-, wires or conductors, series-connected with the 
junction boxes, and employed in connection with suit- 
able voltmeters, to indicate the pressure at the junction 
boxes. 

The pressure ^vires are sometimes called the pilot 
wires. 

WIRING— Collectively the wires or conducting circuits used 
in any sj^stem of electric distribution. 

WORK — The product of the force by the distance through 
which the force acts. • 

A force whose intensity is equal to one pound acting 
through the distance of one foot, does an amonnt of 
work equal to one foot-pound. 

WORK, ELECTRIC— The joule. (See Joule). 
1 joule equals 1 watt for 1 second. 

WORK, ELECTRIC, UNIT OF— The volt-coulomb or joule. 
The product of the volts by the coulombs. 

WORKING, PARALLEL, OF DYNAMO-ELECTRIC MA- 
CHINES — The operation of -working several dynamo- 
electric machines as a single source, by connecting 
them with one another in parallel or multiple arc. 



I 



YOKE FIELD— That part of the field magnet frame con- 
necting two magnet cores. 

YOKE, MULTIPLE-BRUSH— A term sometimes applied to 
multiple brush rocker of a dynamo or motor. 



459 ZIN 

z 

ZINC, AMALGAMATION OF— The covering or amalgama- 
tion of zinc with a layer of mercury. 

ZINC, CP.OW-I'OOT— A crow-foot-shaped zinc used in the 
gravity voltaic cell. 



^ 



INDEX TO TABLES. 

I. Properties of Copper Wire 13-14 

II. Currents Allowed in Wires by Fire Underwriters... . 16 

III. Electro-chemical Series of the Elements 26 

IV. Data of Common Batteries 30 

V. Properties of MetaiS 34 

VI. Permeability Table 67 

VII. Magnetic Traction or Pull 83 

VIII. Magnetic Circuits of Dynamos 91 

IX. Hysteresis in Soft Iron 131 

X. Dynamo and Motor Windings 165-167 

XI. Tensile Strength of Copper Wire 292 

XII. Circumferences of Circles 293 

XIII. Areas of Circles 294-295 

XIV. Areas of Small Circles 296 

XV. Price List Copper Magnet Wire 297 

XVI. Specific Gravities of Metals 298 

XVII. Decimal Equivalents of Parts of an Inch 299 

XVin. Wire Gauges in Mils 300 

XIX. Properties of Aluminum Wire 301-302 

XX. Areas of different Wire Gauges 303 

XXI. Current required by Motors 304 

XXII. Type M. V. Chloride Battery 240 

XXIII. Willard Standard Battery 241 

XXIV. Willard Special Battery 241 

XXV. Edison Battery. 243 



INDEX. 
A 

Active material in storage batteries 239-242 

Alternating currents 219 

Alternating current, advantages of 222 

Alternations 219 

Aluminum wire, table of 301-362 

Amalgamation of battery zincs 29 

Ampere turns required in parts of magnetic circuit 64 

Ampere turns, calculation of from table 67 

Ampere turns, size of wire to produce certain 105 

Analogy between water and electricity i 

Anode 31 

Armature current, division of at brushes 137 

Armature, drum 116 

Armature, gramme ring 112 

Armature, iron clad 66 

Armature reaction 138 

Armature reaction, magnetization of fields by 139 

Armature, smooth core 65 

Armature, tunnel wound 50 

Arc lamps 203 

Automatic rheostat 182 

Automobile battery 238 

Automobile controller 237 

Automobile motor 232 

Automobile, power required for 234 

B 

Battery, automobile 238 

Battery, charging of 243 



464 



Battery, Chloride . . 239 

Battery, Edison 242 

Battery for experimental purposes 29 

Battery, storage .- 35 

Battery, storage capacity of 36 

Battery, storage uses of 36 

Batteries, table of data of .' 30 

Battery, troubles 247 

Battery, Willard 240 

Brakes, electric 86 

Brush arc dynamo , 139 

Brush arc motor 127 

Brushes, inertia of 190 

Brushes, position of in multipolar motors 112 

Brushes, sparking affected by position of 146 

c 

Calculation of ampere turns from table 72 

Carbon brush 148 

Carbon as positive element in battery ceil 28 

Capacity of storage batteries 35 

Cathode 31 

Charging of automobile batteries 243 

Chloride accumulator 239 

Circuits, primary 227 

Circuits, secondary 227 

Commutation, conditions of perfect 146-149 

Commutator, vibration of 190 

Compass, mariner*s , 40 

Compound winding 170 

Compound winding, number of series turns 181 

Connections of armature and field magnets 177 

Constant potential system 20 



465 



Constant voltage, effect on life of lamps 202 

Controller connections for automobiles 336 

Copper wire, change of resistance with temperature .... 100 

Counter E. M. F., identity with primary 123 

Current required by motors 304 

Current, three-phase 224 

Current, two-phase 222 

Cycle 219 

Cycle, per second 221 

D 

Density of electrolyte in batteries 246 

Direction of flow of current 31 

Drop allowed in street railway feeders 18 

Drum armature 116 

Drum armature, winding of 150 

E 

Earth as magnet • 40 

Eddy currents 133 

Edison battery 241 

Edison current meter . 31 

Edison dynamo, leakage co-efificient of 90 

Electric brakes 86 

Electrolyte 247-247 

Electro-magnet 43 

Electropeon fluid for batteries 29 

Electro-plating *. 32 

E. M. F., counter 123 

E. M. F., productior of in armatures Ii2 

E. M. F., winding for different 117 

Enclosed arc lamps 202 

Energy formulae ,..,,,,,.,,...,..,,.?•??• ^ ,. » 95 



466 

Energy in electric circuits 95 

F 

Feeders for street railway work 18 

Field coil, improper connection of 196 

Field coil, heating of 196 

Field coil, open circuit in 194 

Field coil, short circuit in 195 

Field discharge 178 

Field, distortion of by armature reaction 141 

Field magnets , 175 

Flow of current, direction of 31 

Force, field of 41 

Force, field of, strength in the U. S 41 

Force, line of 41 

Force, mechanical, exerted on wire carrying current in 

magnetic field 49 

Friction between brush and commutator. 102 

G 

Galvani, his discovery 25 

Gramme ring armature 112 

Gramme ring, practical advantage of 116 

Grounds 192 

Grounds, partial 193 

Grounds, permanent 193 

H 

Heating of commutator 192 

Heating of field coils 196 

Heating of magnet coils 108 

Helix 14 

High voltage, use in transmission of power 99 



467 



Horse power, electrical, equivalent of 95 

Horse power required for automobiles 234 

Horizontal winding 160 

Hydrometer 246 

Hysterisis 130 

Hysterisis in four-pole field 132 

I 

Incandescent lamps, life of 10 

Iron clad armature — 66 

L 

Lap winding 162 

Leads, armature 160 

Leakage of magnetic lines 89 

Lentz law 119 

Life of incandescent lamps 10 

Lines of force 41 

M 

Magnet electro 43 

Magnet, field of 45 

Magnet, best design for lifting purposes 84 

IMagnet coils, calculation of 106 

Magnet coils, heating of 124 

Magnetic lines, bunching of 69 

Magnetic lines, leakage of 89 

Magnetic traction 82 

Magnetic spectrum 42 

Magnetic whirl 42 

Magnetic vane voltmeter 214 

Magnetism 40 

Magnetism, residual 175-213 

Magnetization of field by armature reaction 139 



468 



Mariner's compass 40 

Mechanical force exerted on wire carrying current in 

magnetic field ; . . . . 49 

Meter, Brush '. 213 

Meter, Thompson's recording 215 

Meter, Westinghouse 214 

Meter, Western Electric 212 

Meter, Weston 211 

Motor, Baxter 127 

Motor, Brush 127 

Motors, compound wound 170 

Motor, series and properti-es of 125-232 

Motor, shunt wound, speed of 124 

Motors 208-211 

Multipolar fields, effect of an armature reaction 100 

N 

Nitrate of soda as electrolyte 28 

Number of bars in commutator 164 

Number of slots in armature 164 

Noise of machine in operation 197 

o 

Ohms law 3 

Open circuits 186 

Open circuits in field coils 194 

Over commutation 127 

P 

Periodicity 221 

Permeability 56 

Plating, electro 32 

Platinum sponge • • . • . 27 



469 



Platinum wire in incandescent lamps 202 

Polarization 26 

Porous cup 27 

Polyphase currents from direct current commutators... 224 

Position of brushes in multipolar machines 162 

Power for automobiles 234 

Power for primary batteries 28 

Primary circuits 227 

R 

Residual magnetism 175 

Resistance of brush contact 147 

Resistance of copper wire, change of with temperature 106 

Resistance of copper wire, rule for 20 

Revolving pole 224 

Rheostat 177 

Rhumkorf coil 228 

S 

Saturation of magnetic circuit 56 

Secondary circuits 227 

Self induction 145 

Series arc lamps 205 

Series system of arc lighting 20 

Series wound motor, properties of 125 

Short circuits 187 

Shunt motor proper, connection of 181 

Shunt wound motor, constant speed of 124 

Sine wave 221 

Smee battery 27 

Smooth core armature -. . . 65 

Solenoid 45 

Solenoid meter 216 



470 



Solid pole pieces, eddy currents in 134 

Sparking 144-189 

Spectrum magnetic 42 

Starting box, automatic 182 

Starting box, overload 183 

Steel ingots handled by means of magnet 86 

Storage batteries 35-238 



Thompson recording meter 215 

Three-phase current 226 

Transformers ^ 227 

Transmission of power by alternating currents 228 

Traction magnetic 82 

Transmission of power, connection with high voltage. . . 98-99 

Transmission of power, weight of copper 99 

Tungsten steel 210-240 

Tunnel wound armature 50 

Two phase current 224 

V 

Vacuum 201 

Vertical winding 160 

Voltage constant, effect on life of incandescent lamps. . 202 

Voltage of storage battery * 4-245 

Volta's battery 25 

Voltameter 31 

Volt-meter, Weston 207 

W 

Watts, mechanical equivalent of 25 

Watts, radiated from armature 106 

Watts, radiated from field coil 107 



471 



Watts required for incandescent lamps 263 

Wave sine 221 

Wave winding 161 

Weston meters 207-208 

Willard storage battery 250 

Windings, armature 165 

Winding lap 162 

Wire winding, armature, arrangement of 158 

Wire on dynamo, office of 157 

Wiring for equal drop 17 

Wood arc dynamo » o 139 



Repair Work 



On the following page will be 
found our prices for rewinding 
armatures. 

For 14 years we have made a 
specialty of this branch of electrical 
repairing. 

We can rewind any kind of an 
armature, none too complicated for 
us to handle. 

Our long experience and responsi- 
bility, we feel, warrants your 
patronage. 

Cleveland Armature Works 

CLEVELAND, OHIO 



Price List for Winding Armatures 



RAILWAY GENERATOR ARMATURES 

Discount from these prices according 
to type. 



15 Kilowatt, 500 volt 

20 

£0 

45 

60 



90 
100 
150 
175 
200 



. $ 50 00 

. 66 00 

. 77 00 

. 94 00 

. 105 00 

. 115 00 

. 132 00 

. 148 00 

. 154 00 

. 19S 00 

. 214 00 

. 231 00 



Larger sizes speciallj' quoted. 

RAILWAY MOTOR ARMATURES. 

Discount from these prices according to 

type, and whether drum or 

coil wound. 

10 H. P., 500 volt $ 31 00 

15 '• " 47 00 

20 " " ... 50 00 

25 " " 53 00 

30 " " 58 00 

50 " " 75 00 

100 " " 121 00 

Our prices for Railway Armature 

Coils will interest you. 

(We make them for every system.^ 

STATIONARY MOTOR ARMATURES 

Discount from these prices according to 
type and voltage. 

Commutators Armatures 

Refilled Rewound 

^ H. P $ 4 25 $ 7 00 

J/i " 4 50 10 00 

Vi '' 5 00 14 00 

1 " 5 70 16 00 

\V2 '' 7 00 17 25 

2 " 8 00 20 00 

3 " 9 25 24 50 

5 •• 11 00 28 00 

6 " 13 00 29 00 

IV2 '' 15 50 30 00 

10 * ' IS 50 33 00 



Stationary Motor Armatures- 
15 H. P $20 25 



20 
25 
30 
40 
50 



24 50 
30 75 
35 00 
43 00 
52 00 



-Con'd 

s^39 00 

44 00 

50 00 

60 00 

69 00 

77 00 



INCANDESCENT DYNAMO ARMATURES 

Discount from these prices according 
to type. 
Commutators 
Refilled 

lights $ 6 50 

8 25 



15 

25 

50 

75 

100 

150 

200 

250 

300 

400 

500 

600 

800 

1000 



10 50 
14 00 
16 75 
19 25 
21 25 
25 00 
30 75 
37 00 
45 00 
52 00 
63 00 
75 00 



Armatures 
Rewound 
$ 17 00 
20 00 
26 00 
29 00 
32 00 
36 00 
41 00 
45 00 
50 00 
63 00 
71 00 
77 00 
85 00 
100 00 



ALTERNATOR ARMATURES 

Discount from these prices according 

to type. 
500 lights $40 00 



650 
800 
1000 
1200 
1350 
2000 



42 00 
49 00 
59 00 
65 00 
68 00 
S3 00 



ARC ARMATURES 

Discount from these prices according to 

type, and whether drum or coil 

wound and voltage. 

30 lights $150 00 



35 
50 
60 
80 
100 



158 00 
195 00 
215 00 
235 00 
255 00 



Write for Discount, giving: make and capacity of Machine 

CLEVELAND ARMATURE WORKS, Cleveland, Ohio 



mxc c. A. ^v. 




Type A 



Dynamos and Motors 

Manufactured by 

Cleveland Armature nV orks 

CLEVELAND. OHIO 



A /IVCADC^^ experience in repairing most all 
I ^li I nAll J ^^^ diiferent makes of Dynamos and 

A j[ "Motors should be sufficient to enable 

a man of only ordinary intellect to 
detect the strong and weak points and to correct same 
in a machine of his own design. W^e ask permission to 
ship you one of our Dynamos 6r Motors subject to your 
approval and acceptance after 30 days' trial. Considering 
price alone, they are not cheap — but considering quality 
and price, they are the cheapest machines on the market. 
In writing for quotations, mention speed required. 



MOTORS 


DYNAMOS 


Shipping 
Weight 
in Box 


Pulley 


H. P. 


Speed 

liOand 

220 volts 


Speed 
500 
volts 


K.W. 


16 
C.P. 
Lamp 

9 


Speed 

110 to 

115 volts 


c 

5 


1 


14 


1400 


1700 


.5 


1550 


180 


3J/. 


3 


1 


1800 


2200 


1.0 


18 


2000 


180 


3K2 


3 





1100 


130i) 


1.9 


35 


1300 


250 


4 


3 


3 


1900 


2100 


2.75 


50 


2100 


250 


4 


3 


3 


1050 


1250 


2.75 


50 


1250 


425 


4 


iV2 


4 


1600 


1850 


3.50 


60 


1850 


425 


4 


Wz 


5 


1050 


1250 


4.5 


80 


1250 


625 


5 


5 


7'A 


1650 


1(375 


6.25 


110 


1675 


625 


5 


5 


T^-S 


1000 


1150 


6.25 


110 


1150 


775 


6 


5K> 


10 


1500 


1650 


8.50 


155 


1650 


775 


6 


5'< 


10 


900 


1050 


8.50 


155 


1050 


995 


6 


5!i 


r2K. 


1200 


1350 


10.50 


190 


1350 


995 


6 


hVi 


1-2% 


800 


900 


10.50 


190 


900 


1300 


7 


6K' 


15 


1200 


1350 


12.50 


230 


1350 


1300 




6J/. 


15 


700 


800 


12.50 


230 


800 


1G25 


10 


8 


•20 


1050 


1200 


16.75 


310 


1200 


1625 


10 


8 



XoS Cleveland Armature Works 

to Agents CLEVELAND, OHIO 



APB 1 "" 



>k. 



f 



One copy del. to Cat. Div. 



^ APR U 1911 



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